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Article

Photocatalytic Synthesis of 6-Phosphorylated Phenanthridines from 2-Isocyanobiphenyls via Radical C−P and C−C Bond Formation

by
Liping Wang
1,
Qin Zhang
2,
Xiaoyan Sang
1 and
Qiuping Ding
1,*
1
National Engineering Research Center for Carbohydrate Synthesis, Key Lab of Fluorine and Silicon for Energy Materials and Chemistry of Ministry of Education, Key Laboratory for Green Chemistry of Jiangxi Province, Jiangxi Normal University, Nanchang 330022, China
2
Basic Geological Survey Institute of Jiangxi Geological Survey Institute, Nanchang 330201, China
*
Author to whom correspondence should be addressed.
Catalysts 2023, 13(7), 1036; https://doi.org/10.3390/catal13071036
Submission received: 11 May 2023 / Revised: 21 June 2023 / Accepted: 22 June 2023 / Published: 25 June 2023
(This article belongs to the Special Issue Catalyzed Carbon-Heteroatom Bond Formation)
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Abstract

:
A mild, efficient, photocatalytic synthesis of 6-phosphorylated phenanthridines via tandem radical addition/cyclization/aromatization of 2-isocyanobiphenyls with diarylphosphine oxides is reported. The method features operational simplicity in metal-free conditions, using low-cost Rose Bengal as a catalyst and sustainable air as a terminal oxidant at room temperature and providing the desired products in moderate to good yields.

Graphical Abstract

1. Introduction

Phenanthridine is a significant fused N-heterocycle, which is ubiquitous in many bioactive alkaloids, pharmaceuticals, natural products, and functional material molecules [1,2,3]. For example, nitidine chloride (Figure 1) is an active, natural anticancer product with a phenanthridine motif that has been found to inhibit topoisomerase I and topoisomerase II [4]. NK109 (Figure 1) has been found to exhibit antitumor effects against a number of human cancer cell lines [5]. Fagaronine (Figure 1) is an active antileukemic and antimalarial alkaloid [6]. In addition, trispheridine [7], N-methylcrinasiadine [8], and lycobetaine [9] are natural alkaloids with excellent bioactivities (Figure 1).
Extensive studies and improvements upon the synthesis of highly functionalized phenanthridine derivatives have been conducted due to their important biological activities. Great progress and developments have been made in the synthetic strategies of phenanthridine derivatives via C-H bond activation, radical addition cyclization, photochemical catalysis, isocyanide chemistry, etc. [10,11,12]. The transformation proceeded in the absence or presence of various transition-metal catalysts, such as Pd, Mn, Cu, Ru, Ir, Rh, Fe, Ni, and so on. The functionalization mainly focused on the 6-position of phenanthridine [10,11,12], including trifluoromethylation, difluoromethylation, arylation, alkylation, alkynylation, acylation, sulfonylation, phosphorylation, difluoromethylphosphonation, benzylation, trichooromethylation, thiolation, etc.
C-P bond construction has attracted dramatic attention due to the potential applications of organophosphorous compounds in pharmaceutical chemistry and materials science [13,14]. In 2014, several methods for the synthesis of 6-phosphorylated phenanthridines initiated by Ag(I) or Mn(III) salts were reported via radical cascade cyclization (Scheme 1, eq(a–e)) [15,16,17,18,19]. In 2016, Lakhdar and coworkers described the 6-phosphorylation of phenanthridines in the presence of diphenyliodonium salt and triethylamine under metal-free conditions (Scheme 1, eq(f)) [20]. Subsequently, several photocatalytic methods were reported in the presence of photocatalyst [Ir(ppy)2(dtbpy)]PF6 [21]/2D-COF-1 [22]/4CzIPN-tBu [23] using K2S2O8 or TBHP as an oxidant (Scheme 1, eq(g–i)).
Recently, we have described the synthesis of 6-aroyl [24] and 6-benzylated [25] phenanthridines via the iron-catalyzed cascade radical addition/cyclization of 2-biphenyl isocyanides. In 2019, we reported a visible-light-induced Mn(acac)3-catalyzed method for the synthesis of 6-β-keto alkyl phenanthridines in the absence of an extended oxidant [26]. In addition, we also described a Mn(III)-catalyzed radical process of 2-isocyanobiphenyls for the synthesis of 6-phosphorylated phenanthridines [16]. Herein, we report another alternative method for the preparation of 6-phosphorylated phenanthridines using low-cost Rose Bengal as a catalyst and sustainable air as a terminal oxidant under metal-free conditions at room temperature.

2. Results and Discussion

Initially, 2-isocyano-5-methyl-1,1′-biphenyl, 1a, and diphenylphosphine oxide, 2a, were chosen as model reaction substrates for the optimization conditions. The desired product, 3aa, was isolated in 15% yield using Rose Bengal (2 mol%) as a catalyst and DBU as a base in the co-solvent MeCN/H2O at room temperature under an air atmosphere (Table 1, entry 1). Increasing the loading of catalyst to 5–10 mol% improved the yields of 3aa (Table 1, entries 2 and 3). With an increase in the diphenylphosphine oxide (2a) amount from 1.5 equiv to 3.5–4.5 equiv, the results showed that the yields of target product 3aa raised obviously (Table 1, entries 4 and 5). Then, we screened several other organic photocatalysts, and the results showed that Eosin Y could promote the reaction smoothly and provide 3aa in a 61% yield, while only trace amounts of the desired product 3aa were observed when Fluorescein and Rhodamine B were used as photocatalysts (Table 1, entries 6–8). In addition, a series of bases involving Et3N, DABCO, Na2CO3, and K2CO3 were surveyed, but no better yield was obtained (Table 1, entries 9–12). Then we attempted to change the amount of base, and the best result (84%) was obtained in the presence of a 3.0 equivalent of DBU (Table 1, entries 13–15). The examination of the reaction medium showed that the effect of the solvent is obvious. The reaction could not offer a better yield in pure acetonitrile or other co-solvents, such as MeOH/H2O, EtOH/H2O, and THF/H2O (Table 1, entries 16–19). The control experiment indicated that the irradiation of blue LED lights is important because no reaction was carried out in the dark (Table 1, entry 20). Unfortunately, the present method was not suitable for the multigram scale. When the reaction carried out on 6 mmol scale, only 15% of the desired product 3aa was isolated (Table 1, entry 14).
We next examined the generality and the substrate scope of 2-isocyanobiphenyls under the optimized reaction conditions (Scheme 2). Initially, the electronic effect of the substituents R2 was investigated. The reaction could tolerate both electron-donating groups and electron-withdrawing groups, such as methyl, methoxy, halogen (F, Cl), and trifluoromethyl on the ortho-, meta-, or para-position of the phenyl ring, providing the corresponding products in moderate to good yields. For instance, ortho-methyl-substituted substrate 1b gave the target product 3ba in 74% yields. Meta-methyl-substituted substrate 1c provided two isomers, 3ca and 3ca’, in 60% total yields in a ratio of about 1:1. Para-trifluoromethyl-substituted substrate 1i provided the product 3ia in a 53% yield under standard conditions. Unfortunately, when substrate 1n was used, bearing a nitro group, only a trace amount of desired product was observed under the same conditions. Then, 2-(2-isocyanophenyl)naphthalene was applied to the reaction with 2a, and the product 3pa was obtained in a low yield (38%). The electronic effect of substituent R1 was significant, and the substrates with electron-withdrawing groups of halogens (F, Cl) provided the corresponding products 3ra–3ta in moderate yields of 37–46%. The reaction did not work when substate 1u bore a strong electron-withdrawing group (-CF3). In addition, ortho-methyl (R1)-substituted 2-isocyanobiphenyl 1c also did not work, maybe due to the steric hindrance.
In addition, the substrate scope of diphenylphosphine oxides (2) were also examined under the optimal conditions (Scheme 3). The results shown that the electronic effect was not obvious; diaryl-substituted phosphine oxides (2) with both electron-donating groups and electron-withdrawing groups were proceeded smoothly, providing the corresponding phosphorylation phenanthridines in good yields. Product 3ad was isolated only in moderate yield (46%) due to the steric effect. However, no target product was observed in the case of diisopropyl phosphine oxide 2i.
A control experiment was executed to investigate the possible reaction mechanism (Scheme 4). The reaction was totally inhibited in the presence of the radical scavenger of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO, 3.5 equiv) under standard reaction conditions. The results indicated that the transformation probably underwent cascade radical addition/cyclization processes [10,11,12,24,25,26].

3. Materials and Methods

3.1. General Information

Nuclear magnetic resonance (NMR) spectra were recorded in parts per million from internal tetramethylsilane on the δ scale. 1H and 13C NMR spectra were recorded on a Bruker AV-400 spectrometer operating at 400 MHz and 100 MHz (Bruker, Ettlingen, Germany), respectively. All chemical shift values are quoted in ppm and coupling constants are quoted in Hz. High-resolution mass spectrometry (HRMS) spectra were obtained on a micrOTOF II instrument (Bruker Daltonik GmbH, Bremen, Germany). The characterization (1H- and 13C-NMR and 31P-NMR) for products 3 are provided (see Support Information).

3.2. General Procedure for the Photocatalytic Synthesis of 6-Phosphorylated Phenanthridines from 2-Isocyanobiphenyls

Added to a 25 mL quartz test tube containing a magnetic stir bar were 2-biphenyl isocyanides (1) (0.2 mmol), Rose Bengal (0.01 mmol, 5 mol%), DBU (3.0 equiv) under air, diphenylphosphine oxides (2) (0.6 mmol, 3.0 equiv), and MeCN/H2O (1.0/0.18 mL). The resulting mixture was stirred at room temperature under 30 W blue LED irradiation for 5 h. After completion, monitored by TLC, evaporation of the solvent under reduced pressure followed purification by silica gel chromatography using ethyl acetate–petroleum ether (1:3) as an eluent to provide the desired products (3).

3.3. Characterization Data for Products 3

(2-Methylphenanthridin-6-yl)diphenylphosphine oxide [16,18] (3aa): Isolated (Rf = 0.6, EtOAc—petroleum ether = 1:3) as a white solid (66.1 mg, 84% yield), mp: 222–223 °C. 1H NMR (400 MHz, CDCl3) δ 9.48 (d, J = 8.4 Hz, 1H), 8.57 (d, J = 8.4 Hz, 1H), 8.31 (s, 1H), 8.05–7.84 (m, 5H), 7.76 (t, J = 7.6 Hz, 1H), 7.63 (t, J = 7.6 Hz, 1H), 7.52–7.37 (m, 7H), 2.57 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 155.6 (d, JC-P = 128.7 Hz), 141.3 (d, JC-P = 23.3 Hz), 139.1, 133.1 (d, JC-P = 104.0 Hz), 132.4, 132.3 (d, JC-P = 9.1 Hz), 131.6 (d, JC-P = 2.5 Hz), 130.9, 130.8, 130.5, 128.5, 128.2 (d, JC-P = 12.1 Hz), 127.9, 127.7, 124.2 (d, JC-P = 2.4 Hz), 122.1, 121.7, 22.2. 31P NMR (162 MHz, CDCl3) δ 28.2. HRMS (ESI): m/z [M + H]+ calcd for C26H21NOP: 394.1355, found: 394.1358.
(2-Methylphenanthridin-6-yl)di-p-tolylphosphine oxide (3ab): Isolated (Rf = 0.4, EtOAc—petroleum ether = 1:3) as a white solid (64.1 mg, 76% yield), mp: 249–251 °C. 1H NMR (400 MHz, CDCl3) δ 9.45 (d, J = 8.0 Hz, 1H), 8.63 (d, J = 8.4 Hz, 1H), 8.37 (s, 1H), 7.95 (d, J = 8.4 Hz, 1H), 7.87–7.73 (m, 5H), 7.65 (t, J = 7.6 Hz, 1H), 7.52 (dd, J = 8.4, 0.8 Hz, 1H), 7.26–7.21 (m, 4H), 2.63 (s, 3H), 2.37 (s, 6H). 13C NMR (100 MHz, CDCl3) δ 156.0 (d, JC-P = 128.4 Hz), 141.9 (d, JC-P = 2.7 Hz), 141.2 (d, JC-P = 23.4 Hz), 138.9, 132.3 (d, JC-P = 9.5 Hz), 130.9, 130.4, 130.0 (d, JC-P = 106.4 Hz), 128.9 (d, JC-P = 12.5 Hz), 128.6, 127.9 (d, JC-P = 23.0 Hz), 127.7, 124.2, 122.0, 121.6, 22.2, 21.6. 31P NMR (162 MHz, CDCl3) δ 28.8. HRMS (ESI): m/z [M + H]+ calcd for C28H25NOP: 422.1668, found: 422.1670.
(2-Methylphenanthridin-6-yl)di-m-tolylphosphine oxide (3ac): Isolated (Rf = 0.4, EtOAc—petroleum ether = 1:3) as a white solid (56.5 mg, 67% yield), mp: 237–239 °C. 1H NMR (400 MHz, CDCl3) δ 9.38 (d, J = 8.4 Hz, 1H), 8.50 (d, J = 8.4 Hz, 1H), 8.24 (s, 1H), 7.85 (d, J = 8.4 Hz, 1H), 7.76–7.64 (m, 3H), 7.62–7.51 (m, 3H), 7.41 (d, J = 8.3 Hz, 1H), 7.23–7.17 (m, 4H), 2.50 (s, 3H), 2.25 (s, 6H). 13C NMR (100 MHz, CDCl3) δ 155.8 (d, JC-P = 128.1 Hz), 141.3 (d, JC-P = 23.2 Hz), 139.0, 138.0 (d, JC-P = 11.9 Hz), 133.0 (d, JC-P = 104.4 Hz), 132.6 (d, JC-P = 8.9 Hz), 132.4 (d, JC-P = 2.7 Hz), 132.3 (d, JC-P = 6.8 Hz), 130.9, 130.7, 130.4, 129.5 (d, JC-P = 9.3 Hz), 128.6, 128.1, 128.0 (d, JC-P = 12.8 Hz), 127.7, 124.2 (d, JC-P = 2.4 Hz), 122.1, 121.7, 22.2, 21.5. 31P NMR (162 MHz, CDCl3) δ 28.6. HRMS (ESI): m/z [M + H]+ calcd for C28H25NOP: 422.1668, found: 422.1671.
(2-Methylphenanthridin-6-yl)di-o-tolylphosphine oxide (3ad): Isolated (Rf = 0.4, EtOAc—petroleum ether = 1:3) as a white solid (38.8 mg, 46% yield), mp: 228–230 °C. 1H NMR (400 MHz, CDCl3) δ 9.11 (d, J = 8.4 Hz, 1H), 8.58 (d, J = 8.4 Hz, 1H), 8.31 (s, 1H), 7.73 (d, J = 8.0 Hz, 2H), 7.54 (t, J = 7.6 Hz, 1H), 7.42 (d, J = 8.0 Hz, 1H), 7.36–7.26 (m, 4H), 7.24–7.18 (m, 2H), 7.07 (t, J = 7.2 Hz, 2H), 2.55 (s, 3H), 2.36 (s, 6H). 13C NMR (100 MHz, CDCl3) δ 156.1 (d, JC-P = 128.3 Hz), 143.4 (d, JC-P = 7.8 Hz), 141.3 (d, JC-P = 23.5 Hz), 139.1, 133.1 (d, JC-P = 11.9 Hz), 132.4 (d, JC-P = 6.5 Hz), 131.8 (d, JC-P = 2.5 Hz), 131.6, 131.5, 131.1, 130.7, 130.5, 130.4, 128.8, 127.7, 127.6 (d, JC-P = 23.0 Hz), 125.3 (d, JC-P = 12.8 Hz), 124.3, 122.2, 121.6, 22.2, 22.0, 22.0. 31P NMR (162 MHz, CDCl3) δ 38.2. HRMS (ESI): m/z [M + H]+ calcd for C28H25NOP: 422.1668, found: 422.1673.
Bis(3,5-dimethylphenyl)(2-methylphenanthridin-6-yl)phosphine oxide (3ae): Isolated (Rf = 0.5, EtOAc—petroleum ether = 1:3) as a white solid (54.8 mg, 61% yield). mp: 265–268 °C. 1H NMR (400 MHz, CDCl3) δ 9.46 (d, J = 8.4 Hz, 1H), 8.62 (d, J = 8.4 Hz, 1H), 8.36 (s, 1H), 7.97 (d, J = 8.4 Hz, 1H), 7.80 (t, J = 7.4 Hz, 1H), 7.65 (t, J = 7.4 Hz, 1H), 7.55–7.50 (m, 5H), 7.12 (s, 2H), 2.62 (s, 3H), 2.30 (s, 12H). 13C NMR (100 MHz, CDCl3) δ 156.0 (d, JC-P = 127.6 Hz), 141.2 (d, JC-P = 23.2 Hz), 138.9, 137.7 (d, JC-P = 12.6 Hz), 133.4 (d, JC-P = 2.8 Hz), 132.9 (d, JC-P = 104.5 Hz), 132.3 (d, JC-P = 6.8 Hz), 131.0, 130.5 (d, JC-P = 30.6 Hz), 129.9 (d, JC-P = 9.2 Hz), 128.2 (d, JC-P = 100.6 Hz), 128.0 (d, JC-P = 23.0 Hz), 124.2 (d, JC-P = 2.4 Hz), 122.0, 121.6, 22.2, 21.4. 31P NMR (162 MHz, CDCl3) δ 29.0. HRMS (ESI): m/z [M + H]+ calcd for C30H29NOP: 450.1981, found: 450.1986.
Bis(3-methoxyphenyl)(2-methylphenanthridin-6-yl)phosphine oxide (3af): Isolated (Rf = 0.6, EtOAc—petroleum ether = 1:3) as a yellow solid (60.7 mg, 67% yield), mp: 241–243 °C. 1H NMR (400 MHz, CDCl3) δ 9.33 (d, J = 8.0 Hz, 1H), 8.51 (d, J = 8.2 Hz, 1H), 8.25 (s, 1H), 7.85 (d, J = 8.4 Hz, 1H), 7.69 (t, J = 7.6 Hz, 1H), 7.55 (t, J = 7.6 Hz, 1H), 7.49–7.40 (m, 3H), 7.36 (d, J = 7.6 Hz, 1H), 7.33 (d, J = 8.0 Hz, 1H), 7.27–7.18 (m, 2H), 6.93 (d, J = 7.6 Hz, 2H), 3.68 (s, 6H), 2.51 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 159.3 (d, JC-P = 15.0 Hz), 155.4 (d, JC-P = 129.3 Hz), 141.2 (d, JC-P = 23.5 Hz), 139.1, 134.2 (d, JC-P = 103.4 Hz), 132.3 (d, JC-P = 6.8 Hz), 130.9, 130.8, 130.5, 129.3 (d, JC-P = 14.3 Hz), 128.4, 127.9 (d, JC-P = 23.5 Hz), 127.7, 124.7 (d, JC-P = 9.2 Hz), 124.3, 122.1, 121.7, 118.0 (d, JC-P = 2.5 Hz), 117.0 (d, JC-P = 10.1 Hz), 55.4, 22.2. 31P NMR (162 MHz, CDCl3) δ 28.2. HRMS (ESI): m/z [M + H]+ calcd for C28H25NO3P: 454.1567, found: 454.1568.
Bis(3-fluorophenyl)(2-methylphenanthridin-6-yl)phosphine oxide (3ag): Isolated (Rf = 0.5, EtOAc—petroleum ether = 1:3) as a yellow solid (58.4 mg, 68% yield), mp: 257–259 °C. 1H NMR (400 MHz, CDCl3) δ 9.44 (d, J = 8.4 Hz, 1H), 8.67 (d, J = 8.4 Hz, 1H), 8.40 (s, 1H), 7.98 (d, J = 8.4 Hz, 1H), 7.86 (t, J = 7.6 Hz, 1H), 7.77–7.62 (m, 5H), 7.58 (d, J = 8.0 Hz, 1H), 7.48–7.40 (m, 2H), 7.22 (td, J = 8.4, 2.0 Hz, 2H), 2.65 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 161.4 (dd, JC-F = 247.9, JC-P = 17.0 Hz Hz), 160.0, 153.4 (d, JC-P = 131.6 Hz), 140.1 (d, JC-F = 23.9 Hz), 138.5, 134.4 (dd, JC-P = 103.5, JC-F = 5.6 Hz Hz), 131.4 (d, JC-P = 7.1 Hz), 130.0, 129.8, 129.7, 129.2 (d, JC-F = 7.3 Hz), 129.1 (d, JC-F = 7.3 Hz), 128.3, 128.1, 127.1, 127.0 (d, JC-P = 3.0 Hz), 126.9, 126.8, 123.3, 121.2, 120.7, 118.3 (d, JC-F = 9.9 Hz), 118.1, 118.0 (d, JC-F = 9.1 Hz), 117. 9 (d, JC-P = 2.6 Hz), 21.2. 31P NMR (162 MHz, CDCl3) δ 24.9. HRMS (ESI): m/z [M + H]+ calcd for C26H19F2NOP: 430.1167, found: 430.1169.
(2-Methylphenanthridin-6-yl)di(naphthalen-1-yl)phosphine oxide (3ah): Isolated (Rf = 0.5, EtOAc—petroleum ether = 1:3) as a yellow solid (66.1 mg, 67% yield), mp: 293–296°C. 1H NMR (400 MHz, CDCl3) δ 9.41 (dd, J = 8.2, 2.0 Hz, 1H), 8.49–8.44 (m, 3H), 8.20 (s, 1H), 7.88–7.79 (m, 3H), 7.75–7.72 (m, 4H), 7.69 (d, J = 8.0 Hz, 2H), 7.64 (t, J = 7.6 Hz, 1H), 7.51 (t, J = 7.6 Hz, 1H), 7.41–7.31 (m, 5H), 2.45 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 155.7 (d, JC-P = 129.5 Hz), 141.3 (d, JC-P = 23.4 Hz), 139.2, 134.7 (d, JC-P = 2.3 Hz), 134.0 (d, JC-P = 8.9 Hz), 132.5 (d, JC-P = 7.3 Hz), 132.4 (d, JC-P = 6.9 Hz), 130.9, 130.8, 130.5, 130.4 (d, JC-P = 103.8 Hz), 129.1, 128.5, 128.1, 127.9, 127.8 (2C), 127.7, 127.6, 126.7, 124.3, 122.2, 121.7, 22.2. 31P NMR (162 MHz, CDCl3) δ 28.9. HRMS (ESI): m/z [M + H]+ calcd for C34H25NOP: 494.1668, found: 494.1672.
(2,10-Dimethylphenanthridin-6-yl)diphenylphosphine oxide (3ba): Isolated (Rf = 0.5, EtOAc—petroleum ether = 1:3) as a white solid (60.3 mg, 74% yield), mp: 222–225 °C. 1H NMR (400 MHz, CDCl3) δ 9.32 (d, J = 8.0 Hz, 1H), 8.52 (s, 1H), 7.89–7.73 (m, 5H), 7.55 (d, J = 7.2 Hz, 1H), 7.46 (t, J = 8.0 Hz, 1H), 7.43–7.37 (m, 3H), 7.37–7.30 (m, 4H), 3.01 (s, 3H), 2.52 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 156.1 (d, JC-P = 129.0 Hz), 142.3 (d, JC-P = 23.8 Hz), 138.0, 135.3, 135.0, 133.2 (d, JC-P = 104.3 Hz), 132.3 (d, JC-P = 9.1 Hz), 131.9 (d, JC-P = 6.7 Hz), 131.6 (d, JC-P = 2.5 Hz), 131.2, 129.5, 129.3 (d, JC-P = 23.4 Hz), 128.1 (d, JC-P = 12.1 Hz), 127.2, 127.0, 126.4, 125.7 (d, JC-P= 2.4 Hz), 27.1, 22.5. 31P NMR (162 MHz, CDCl3) δ 29.4. HRMS (ESI): m/z [M + H]+ calcd for C27H23NOP: 408.1512, found: 408.1515.
(2,8-Dimethylphenanthridin-6-yl)diphenylphosphine oxide (3da): Isolated (Rf = 0.5, EtOAc—petroleum ether = 1:3) as a white solid (48.1 mg, 64% yield), mp: 231–233 °C. 1H NMR (400 MHz, CDCl3) δ 9.28 (s, 1H), 8.48 (dd, J = 8.4, 1.2 Hz, 1H), 8.29 (s, 1H), 7.97–7.87 (m, 5H), 7.61 (dd, J = 8.4, 1.2 Hz, 1H), 7.53–7.36 (m, 7H), 2.58 (s, 3H), 2.53 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 155.0 (d, JC-P = 129.0 Hz), 140.9 (d, JC-P = 23.4 Hz), 139.0, 137.9, 133.6 (d, JC-P = 104.0 Hz), 132.7, 132.4 (d, JC-P = 9.1 Hz), 131.5 (d, JC-P = 2.6 Hz), 130.8, 130.2 (d, JC-P = 6.9 Hz), 130.0, 128.4, 128.1 (d, JC-P = 12.0 Hz), 127.6, 124.3 (d, JC-P = 2.5 Hz), 122.0, 121.5, 22.2, 21.9. 31P NMR (162 MHz, CDCl3) δ 28.0. HRMS (ESI): m/z [M + H]+ calcd for C27H23NOP: 408.1512, found: 408.1516.
Diphenyl(2,7,9-trimethylphenanthridin-6-yl)phosphine oxide (3ea): Isolated (Rf = 0.5, EtOAc—petroleum ether = 1:3) as a white solid (62.3 mg, 74% yield), mp: 255–257 °C. 1H NMR (400 MHz, CDCl3) δ 8.21 (s, 2H), 7.72–7.65 (m, 4H), 7.51 (d, J = 8.0 Hz, 1H), 7.40–7.35 (m, 2H), 7.34–7.27 (m, 5H), 7.17 (s, 1H), 2.84 (s, 3H), 2.48 (s, 3H), 2.43 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 155.4 (d, JC-P = 129.9 Hz), 140.5, 139.8 (d, JC-P = 24.1 Hz), 138.9, 137.4, 135.1 (d, JC-P = 106.9 Hz), 134.2 (d, JC-P = 6.7 Hz), 133.3, 132.0 (d, JC-P = 8.9 Hz), 131.1 (d, JC-P = 2.5 Hz), 130.3, 130.2, 128.0 (d, JC-P = 12.1 Hz), 125.7 (d, JC-P = 23.7 Hz), 124.1 (d, JC-P = 2.6 Hz), 121.8, 120.0, 25.0, 22.2, 21.9. 31P NMR (162 MHz, CDCl3) δ 36.2. HRMS (ESI): m/z [M + H]+ calcd for C28H25NOP: 422.1668, found: 422.1672.
(2-Methyl-[1,3]dioxolo[4,5-j]phenanthridin-6-yl)diphenylphosphine oxide (3fa): Isolated (Rf = 0.4, EtOAc—petroleum ether = 1:1) as a white solid (53.3 mg, 63% yield), mp: 262–265 °C. 1H NMR (400 MHz, CDCl3) δ 8.98 (s, 1H), 8.11 (s, 1H), 7.98–7.84 (m, 6H), 7.54–7.38 (m, 7H), 6.08 (s, 2H), 2.58 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 153.4 (d, JC-P = 131.3 Hz), 151.1, 148.2, 141.0 (d, JC-P = 23.2 Hz), 138.5, 133.8, 132.2 (d, JC-P = 103.9 Hz), 132.3 (d, JC-P = 9.1 Hz), 131.6, 130.7 130.5 (d, JC-P = 7.4 Hz), 129.9, 128.1 (d, JC-P = 12.0 Hz), 125.2 (d, JC-P = 23.4 Hz), 124.4, 121.4, 105.6, 102.0, 99.8, 22.1. 31P NMR (162 MHz, CDCl3) δ 28.1. HRMS (ESI): m/z [M + H]+ calcd for C27H21NO3P: 4038.1254, found: 438.1257.
(9-Chloro-2-methylphenanthridin-6-yl)diphenylphosphine oxide (3ga): Isolated (Rf = 0.4, EtOAc—petroleum ether = 1:3) as a white solid (48.8 mg, 57% yield), mp: 211–214 °C. 1H NMR (400 MHz, CDCl3) δ 9.50 (d, J = 8.8 Hz, 1H), 8.57 (s, 1H), 8.27 (s, 1H), 7.97–7.86 (m, 5H), 7.60 (dd, J = 8.8, 1.6 Hz, 1H), 7.58–7.48 (m, 3H), 7.47–7.41 (m, 4H), 2.62 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 155.3 (d, JC-P = 130.1 Hz), 141.5 (d, JC-P = 22.9 Hz), 139.5, 137.4, 133.8 (d, JC-P = 6.7 Hz), 132.8 (d, JC-P = 104.4 Hz), 132.3 (d, JC-P = 9.2 Hz), 131.8, 131.2, 130.9, 130.2, 128.4, 128.2 (d, JC-P = 12.0 Hz), 126.3 (d, JC-P = 23.4 Hz), 123.2, 121.7 (d, JC-P = 12.1 Hz), 21.2. 31P NMR (162 MHz, CDCl3) δ 27.9. HRMS (ESI): m/z [M + H]+ calcd for C26H20ClNOP: 428.0966, found: 428.0972.
(8-Chloro-2-methylphenanthridin-6-yl)diphenylphosphine oxide (3ha): Isolated (Rf = 0.5, EtOAc—petroleum ether = 1:3) as a white solid (56.5 mg, 66% yield), mp: 229–231 °C. 1H NMR (400 MHz, CDCl3) δ 9.62 (d, J = 2.0 Hz, 1H), 8.46 (dd, J = 8.8, 1.2 Hz, 1H), 8.23 (s, 1H), 8.06–7.90 (m, 5H), 7.69 (dd, J = 8.8, 2.0 Hz, 1H), 7.57–7.47 (m, 3H), 7.46–7.39 (m, 4H), 2.58 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 154.5 (d, JC-P = 128.6 Hz), 141.1 (d, JC-P = 22.7 Hz), 139.7, 133.8, 132.9 (d, JC-P = 104.6 Hz), 132.3 (d, JC-P = 9.1 Hz), 131.8 (d, JC-P = 2.6 Hz), 131.5, 130.9, 130.8, 130.7 (d, JC-P = 6.8 Hz), 128.8 (d, JC-P = 23.1Hz), 128.2 (d, JC-P = 12.1 Hz), 127.5, 123.7, 123.6 (d, JC-P = 2.4 Hz), 121.5, 22.2. 31P NMR (162 MHz, CDCl3) δ 27.2. HRMS (ESI): m/z [M + H]+ calcd for C26H20ClNOP: 428.0966, found: 428.0969.
(2-Methyl-8-(trifluoromethyl)phenanthridin-6-yl)diphenylphosphine oxide (3ia): Isolated (Rf = 0.6, EtOAc—petroleum ether = 1:3) as a yellow solid (48.9 mg, 53% yield), mp: 199–201 °C. 1H NMR (400 MHz, CDCl3) δ 10.00 (s, 1H), 8.70 (d, J = 8.8 Hz, 1H), 8.35 (s, 1H), 8.05–7.95 (m, 6H), 7.60 (d, J = 8.4 Hz, 1H), 7.55–7.48 (m, 2H), 7.47–7.41 (m, 4H), 2.63 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 155.8 (d, JC-P = 127.7 Hz), 141.8 (d, JC-P = 12.5 Hz), 139.9, 134.4 (d, JC-P = 6.2 Hz), 132.8 (d, JC-P = 105.4 Hz), 132.3 (d, JC-P = 9.1 Hz), 131.8 (d, JC-P = 2.6 Hz), 131.7, 131.0, 129.4 (q, JC-F = 32.6 Hz), 128.3 (d, JC-P = 12.1 Hz), 127.3 (d, JC-P = 22.9 Hz), 126.6 (q, 1JC-F = 3.1 Hz), 126.2 (d, JC-P = 4.3 Hz), 123.9 (q, JC-F = 270.8 Hz), 123.2 (d, JC-P = 2.2 Hz), 123.1, 122.0, 22.2. 31P NMR (162 MHz, CDCl3) δ 26.8. HRMS (ESI): m/z [M + H]+ calcd for C27H20F3NOP: 462.1229, found: 462.1232.
(10-Fluoro-2-methylphenanthridin-6-yl)diphenylphosphine oxide (3ja): Isolated (Rf = 0.3, EtOAc—petroleum ether = 1:3) as a white solid (55.1 mg, 67% yield), mp: 192–194 °C. 1H NMR (400 MHz, CDCl3) δ 9.35 (d, J = 8.2 Hz, 1H), 8.78 (s, 1H), 7.96–7.86 (m, 5H), 7.65–7.58 (m, 1H), 7.57–7.48 (m, 4H), 7.47–7.42 (m, 4H), 2.61 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 160.5 (d, 1JC-F = 253.5 Hz), 155.0 (d, JC-P = 129.1 Hz), 141.5 (d, JC-P = 23.0 Hz), 139.8, 132.8 (d, JC-P = 104.8 Hz), 132.3 (d, JC-P = 9.1 Hz), 131.7 (d, JC-P = 2.5 Hz), 130.7 (d, JC-F = 17.7 Hz), 129. 9 (d, JC-F = 24.3), 128.2 (d, JC-P = 12.1 Hz), 128.1 (d, JC-P = 8.9 Hz), 126.6 (d, 2JC-F = 23.0 Hz), 124.6 (d, JC-P = 4.0 Hz), 121.8 (m), 117.3 (d, 2JC-F = 23.2 Hz), 22.4. 31P NMR (162 MHz, CDCl3) δ 28.6. HRMS (ESI): m/z [M + H]+ calcd for C26H20FNOP: 412.1261, found: 412.1267.
(9-Fluoro-2-methylphenanthridin-6-yl)diphenylphosphine oxide (3ka): Isolated (Rf = 0.4, EtOAc—petroleum ether = 1:3) as a white solid (32.1 mg, 39% yield), mp: 205–208 °C. 1H NMR (400 MHz, CDCl3) δ 9.60 (dd, J = 9.2, 6.0 Hz, 1H), 8.23 (s, 1H), 8.21 (d, J = 9.2 Hz, 1H), 7.98–7.89 (m, 5H), 7.57–7.49 (m, 3H), 7.47–7.36 (m, 5H), 2.62 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 163.8 (d, 1JC-F = 251.6 Hz), 155.1 (d, 2JC-P = 128.9 Hz), 141.3 (d, 2JC-F = 23.2 Hz), 139.2, 135.0 (d, JC-P = 9.3 Hz), 134.9 (d, JC-P = 9.3 Hz), 132.9 (d, JC-P = 104.4 Hz), 132.4, 132.3, 131.7 (d, JC-P = 2.7 Hz), 131.6, 131.2, 130.9, 128.2 (d, JC-P = 12.1 Hz), 125.1 (d, 2JC-P = 24.3 Hz), 123.8, 121.8, 116.9 (d, JC-F = 23.3 Hz), 107.2 (d, JC-F = 22.2 Hz), 22.1.31P NMR (162 MHz, CDCl3) δ 27.9. HRMS (ESI): m/z [M + H]+ calcd for C26H20FNOP: 412.1261, found: 412.1265.
(8-Fluoro-2-methylphenanthridin-6-yl)diphenylphosphine oxide (3la): Isolated (Rf = 0.5, EtOAc—petroleum ether = 1:3) as a yellow solid (50.2 mg, 61% yield), mp: 216–219 °C. 1H NMR (400 MHz, CDCl3) δ 9.29 (dd, J = 10.2, 2.6 Hz, 1H), 8.61–8.54 (m, 1H), 8.27 (s, 1H), 7.98–7.90 (m, 5H), 7.56–7.47 (m, 4H), 7.46–7.40 (m, 4H), 2.60 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 161.2 (d, 1JC-F = 247.4 Hz), 154.6 (d, JC-P = 129.2 Hz), 140.9 (d, 2JC-F = 23.5 Hz), 132.8 (d, JC-P = 104.3 Hz), 132.3 (d, JC-P = 9.1 Hz), 131.7 (d, JC-P = 2.5 Hz), 130.9, 130.4, 129.3 (d, 3JC-F = 9.3 Hz), 129.0 (d, 3JC-F = 8.8 Hz), 128.2 (d, JC-P = 12.1 Hz), 124.6 (d, JC-P = 8.5 Hz), 123.9, 121.4 120.3 (d, JC-F = 24.2 Hz), 113.1 (d, 2JC-F = 23.1 Hz), 22.2. 31P NMR (162 MHz, CDCl3) δ 27.4. HRMS (ESI): m/z [M + H]+ calcd for C26H20FNOP: 412.1261, found: 412.1263.
(7,9-Difluoro-2-methylphenanthridin-6-yl)diphenylphosphine oxide (3ma): Isolated (Rf = 0.5, EtOAc—petroleum ether = 1:1) as a white solid (42.9 mg, 50% yield), mp: 245–247 °C. 1H NMR (400 MHz, CDCl3) δ 8.20 (s, 1H), 8.08 (d, J = 9.6 Hz, 1H), 7.80–7.70 (m, 5H), 7.56–7.51 (m, 3H), 7.48–7.43 (m, 4H), 7.04 (t, J = 9.6 Hz, 1H), 2.62 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 163.6 (d, 1JC-F = 252.5 Hz), 160.2 (d, 1JC-F = 246.6 Hz), 141.2, 140.1, 136.1, 133.1 (d, JC-P = 109.2 Hz), 131.9, 131.8, 131.4, 131.3, 130.9, 128.8, 128.0 (d, JC-P = 12.2 Hz), 122.5, 121.9, 104.3 (d, JC-F = 27.2 Hz), 103.9, 22.2. 31P NMR (162 MHz, CDCl3) δ 34.8 (d, J = 4.1 Hz). HRMS (ESI): m/z [M + H]+ calcd for C26H19F2NOP: 430.1167, found: 430.1171.
(3-Methylphenanthridin-6-yl)diphenylphosphine oxide [23] (3oa): Isolated (Rf = 0.4, EtOAc—petroleum ether = 1:3) as a white solid (45.6 mg, 58% yield), mp: 197–200 °C. 1H NMR (400 MHz, CDCl3) δ 9.39 (d, J = 8.0 Hz, 1H), 8.46 (d, J = 8.4 Hz, 1H), 8.32 (dd, J = 8.2, 2.4 Hz, 1H), 7.88–7.80 (m, 4H), 7.72 (s, 1H), 7.68 (t, J = 7.2 Hz, 1H), 7.53 (t, J = 7.6 Hz, 1H), 7.42–7.37 (m, 3H), 7.36–7.30 (m, 4H), 2.42 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 156.7 (d, JC-P = 128.2 Hz), 142.9 (d, JC-P = 23.1 Hz), 139.0, 133.1 (d, JC-P = 104.1 Hz), 132.7 (d, JC-P = 6.9 Hz), 132.3 (d, JC-P = 9.1 Hz), 131.6 (d, JC-P = 2.6 Hz), 130.9, 130.6, 130.5, 128.5, 128.2 (d, JC-P = 12.1 Hz), 127.5 (d, JC-P = 12.6 Hz), 127.4, 122.0 (d, JC-P = 2.5 Hz), 121.9 (d, JC-P = 5.0 Hz), 21.4. 31P NMR (162 MHz, CDCl3) δ 28.1. HRMS (ESI): m/z [M + H]+ calcd for C26H21NOP: 394.1355, found: 394.1358.
Benzo[i]phenanthridin-5-yldiphenylphosphine oxide (3pa): Isolated (Rf = 0.5, EtOAc—petroleum ether = 1:1) as a white solid (32.6 mg, 38% yield), mp: 221–223 °C. 1H NMR (400 MHz, CDCl3) δ 9.40 (d, J = 8.8 Hz, 1H), 9.09–9.06 (m, 1H), 9.05–9.00 (m, 1H), 8.16–8.12 (m, 1H), 8.04–8.00 (m, 1H), 7.98–7.90 (m, 5H), 7.77–7.66 (m, 4H), 7.54–7.40 (m, 6H). 13C NMR (100 MHz, CDCl3) δ 155.3 (d, JC-P = 128.2 Hz), 144.8 (d, JC-P = 23.3 Hz), 133.1 (d, JC-P = 104.6 Hz), 132.4 (d, JC-P = 9.1 Hz), 131.9 (d, JC-P = 6.8 Hz), 131.7, 131.6, 130.9, 128.9, 128.8, 128.7, 128.5, 128.4 (d, JC-P = 2.7 Hz), 128.2 (d, JC-P = 12.0 Hz), 128.1, 127.4 (d, JC-P = 22.6 Hz), 127.2, 126.7, 124.6, 124.0. 31P NMR (162 MHz, CDCl3) δ 29.1. HRMS (ESI): m/z [M + H]+ calcd for C29H21NOP: 430.1355, found: 430.1359.
(10-Methoxyphenanthridin-6-yl)diphenylphosphine oxide (3qa): Isolated (Rf = 0.3, EtOAc—petroleum ether = 1:1) as a white solid (45.9 mg, 56% yield), mp: 244–246 °C. 1H NMR (400 MHz, CDCl3) δ 9.58–9.45 (m, 1H), 9.14 (d, J = 8.2 Hz, 1H), 8.03–7.98 (m, 1H), 7.93–7.86 (m, 4H), 7.72–7.64 (m, 2H), 7.62 (t, J = 8.0 Hz, 1H), 7.53–7.47 (m, 2H), 7.46–7.40 (m, 4H), 7.30 (d, J = 8.0 Hz, 1H), 4.10 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 158.1 (d, JC-P = 2.7 Hz), 156.4 (d, JC-P = 129.1 Hz), 143.3 (d, JC-P = 23.2 Hz), 133.1 (d, JC-P = 104.5 Hz), 132.3 (d, JC-P = 104.5 Hz), 132.3 (d, JC-P = 9.1 Hz), 131.6 (d, JC-P = 2.4 Hz), 130.9, 129.7 (d, JC-P = 23.8 Hz), 128.7, 128.2, 128.1 (d, JC-P = 12.1 Hz), 128.0 (d, JC-P = 5.6 Hz), 124.2, 123.1 (d, JC-P = 7.0 Hz), 120.8, 112.1, 55.8. 31P NMR (162 MHz, CDCl3) δ 29.2. HRMS (ESI): m/z [M + H]+ calcd for C26H21NO2P: 410.1304, found: 410.1309.
(2-Chlorophenanthridin-6-yl)diphenylphosphine oxide [18] (3ra): Isolated (Rf = 0.4, EtOAc—petroleum ether = 1:3) as a white solid (38.1 mg, 46% yield), mp: 241–243 °C. 1H NMR (400 MHz, CDCl3) δ 9.41 (d, J = 8.0 Hz, 1H), 8.48 (d, J = 8.0 Hz, 1H), 8.47 (s), 7.89 (d, J = 8.8 Hz, 1H), 7.86–7.80 (m, 4H), 7.77 (d, J = 8.0 Hz, 1H), 7.64 (t, J = 7.6 Hz, 1H), 7.56 (dd, J = 8.8, 2.0 Hz, 1H), 7.47–7.42 (m, 2H), 7.40–7.34 (m, 4H). 13C NMR (100 MHz, CDCl3) δ 156.3 (d, JC-P = 128.2 Hz), 140.1 (d, JC-P = 23.4 Hz), 138.2, 133.9, 131.6 (d, JC-P = 104.7 Hz), 131.5, 131.3, 131.2, 130.8 (d, JC-P = 2.6 Hz), 130.3, 128.3, 127.7, 127.5, 127.2 (d, JC-P = 12.2 Hz), 124.4, 121.1, 120.7, 113.0. 31P NMR (162 MHz, CDCl3) δ 28.5. HRMS (ESI): m/z [M + H]+ calcd for C25H18ClNOP: 414.0809, found: 414.0813.
(2-Fluorophenanthridin-6-yl)diphenylphosphine oxide [18] (3sa): Isolated (Rf = 0.3, EtOAc—petroleum ether = 1:3) as a yellow solid (31.8 mg, 40% yield), mp: 235–237 °C. 1H NMR (400 MHz, CDCl3) δ 9.41 (d, J = 8.4 Hz, 1H), 8.45 (d, J = 8.0 Hz, 1H), 8.13–8.09 (m, 1H), 7.99–7.93 (m, 1H), 7.86–7.76 (m, 5H), 7.64 (t, J = 7.6 Hz, 1H), 7.48–7.33 (m, 7H). 13C NMR (100 MHz, CDCl3) δ 161.4 (d, JC-F = 248.9 Hz), 155.1 (d, JC-P = 131.7 Hz), 138.6 (d, JC-P = 23.1 Hz), 132.5 (d, JC-P = 9.3 Hz), 131.7 (d, JC-P = 104.3 Hz), 131.2 (d, JC-P = 9.1 Hz), 130.7, 130.1, 127.6 (d, JC-F = 16.3 Hz), 127.2 (d, JC-P = 12.1 Hz), 126.6, 124.9, 121.3, 116.8 (d, JC-F = 24.5 Hz), 106.1 (d, JC-F = 23.2 Hz). 31P NMR (162 MHz, CDCl3) δ 28.5. HRMS (ESI): m/z [M + H]+ calcd for C25H18FNOP: 398.1105, found: 398.1112.
(3-Chlorophenanthridin-6-yl)diphenylphosphine oxide (3ta): Isolated (Rf = 0.4, EtOAc—petroleum ether = 1:3) as a white solid (30.6 mg, 37% yield), mp: 194–197 °C. 1H NMR (400 MHz, CDCl3) δ 9.44 (d, J = 8.4 Hz, 1H), 8.48 (d, J = 8.0 Hz, 1H), 8.40 (d, J = 8.8 Hz, 1H), 7.95 (d, J = 1.6 Hz, 1H), 7.87–7.80 (m, 4H), 7.76 (t, J = 7.6 Hz, 1H), 7.64–7.54 (m, 2H), 7.47–7.41 (m, 2H), 7.41–7.32 (m, 4H). 13C NMR (100 MHz, CDCl3) δ 158.5 (d, JC-P = 125.7 Hz), 143.2 (d, JC-P = 23.4 Hz), 134.5, 132.6 (d, JC-P = 104.5 Hz), 132.2 (d, JC-P = 9.1 Hz), 131.9, 131.5, 130.1, 129.3, 128.8, 128.3 (d, JC-P = 12.3 Hz), 127.8 (d, JC-P = 22.7 Hz), 123.6, 122.9 (d, JC-P = 2.4 Hz), 122.0. 31P NMR (162 MHz, CDCl3) δ 28.3. HRMS (ESI): m/z [M + H]+ calcd for C25H18ClNOP: 414.0809, found: 414.0816.

4. Conclusions

Rose Bengal was found to be an available photocatalyst for the cascade phosphorylation cyclization of 2-isocyanobiphenyls. A wide range of 6-phosphorylated phenanthridines was synthesized efficiently via visible-light-induced radical addition cyclization under metal-free conditions. A biological screening of these P-containing compounds is in progress in our laboratory.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/catal13071036/s1. The experimental procedures and characterization (1H- and 13C-NMR and 31P-NMR) for all of the products are provided in the supporting information.

Author Contributions

Conceptualization, Q.D. and L.W.; methodology, Q.D. and X.S.; validation, L.W. and Q.Z.; writing—original draft preparation, L.W.; writing—review and editing, X.S. and Q.D.; supervision, Q.D. All authors have read and agreed to the published version of the manuscript.

Funding

We gratefully acknowledge the National Natural Science Foundation of China (21961016), the Foundation for Academic and Technical Leaders of Major Disciplines of Jiangxi Province (20225BCJ22007) and the Natural Science Foundation of Jiangxi Province (20224ACB203009) for financial support.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Catalysts 13 01036 g001 550
Figure 1. Representative bioactive phenanthridine derivatives.
Figure 1. Representative bioactive phenanthridine derivatives.
Catalysts 13 01036 g001
Catalysts 13 01036 sch001 550
Scheme 1. Synthesis of 6-phosphorylated phenanthridines from 2-isocyanobiphenyls.
Scheme 1. Synthesis of 6-phosphorylated phenanthridines from 2-isocyanobiphenyls.
Catalysts 13 01036 sch001
Catalysts 13 01036 sch002 550
Scheme 2. Substrate scope of 2-isocyanobiphenyls.
Scheme 2. Substrate scope of 2-isocyanobiphenyls.
Catalysts 13 01036 sch002
Catalysts 13 01036 sch003 550
Scheme 3. Substrate scope of diphenylphosphine oxides.
Scheme 3. Substrate scope of diphenylphosphine oxides.
Catalysts 13 01036 sch003
Catalysts 13 01036 sch004 550
Scheme 4. Control experiment in the presence of TEMPO.
Scheme 4. Control experiment in the presence of TEMPO.
Catalysts 13 01036 sch004
Table
Table 1. Optimization of the reaction conditions a.
Table 1. Optimization of the reaction conditions a.
Catalysts 13 01036 i001
Entry1a/2aCatalystBaseSolventYield (%) b
11/1.5Rose Bengal (2 mol%)DBUMeCN/H2O (1.0/0.18 mL)15
21/1.5Rose Bengal (5 mol%)DBUMeCN/H2O (1.0/0.18 mL)36
31/1.5Rose Bengal (10 mol%)DBUMeCN/H2O (1.0/0.18 mL)32
41/3.5Rose Bengal (5 mol%)DBUMeCN/H2O (1.0/0.18 mL)78
51/4.5Rose Bengal (5 mol%)DBUMeCN/H2O (1.0/0.18 mL)77
61/3.5Eosin Y (5 mol%)DBUMeCN/H2O (1.0/0.18 mL)61
71/3.5Fluorescein (5 mol%)DBUMeCN/H2O (1.0/0.18 mL)trace
81/3.5Rhodamine B (5 mol%)DBUMeCN/H2O (1.0/0.18 mL)trace
91/3.5Rose Bengal (5 mol%)NEt3MeCN/H2O (1.0/0.18 mL)69
101/3.5Rose Bengal (5 mol%)DABCOMeCN/H2O (1.0/0.18 mL)trace
111/3.5Rose Bengal (5 mol%)Na2CO3MeCN/H2O (1.0/0.18 mL)trace
121/3.5Rose Bengal (5 mol%)K2CO3MeCN/H2O (1.0/0.18 mL)trace
131/3.5Rose Bengal (5 mol%)DBU cMeCN/H2O (1.0/0.18 mL)38
141/3.5Rose Bengal (5 mol%)DBU dMeCN/H2O (1.0/0.18 mL)84 (15) g
151/3.5Rose Bengal (5 mol%)DBU eMeCN/H2O (1.0/0.18 mL)80
161/3.5Rose Bengal (5 mol%)DBU dMeCN50
171/3.5Rose Bengal (5 mol%)DBU dEtOH/H2O (1.0/0.18 mL)43
181/3.5Rose Bengal (5 mol%)DBU dMeOH/H2O (1.0/0.18 mL)56
191/3.5Rose Bengal (5 mol%)DBU dTHF/H2O (1.0/0.18 mL)61
20 f1/3.5Rose Bengal (5 mol%)DBUTHF/H2O (1.0/0.18 mL)NR
a Reaction conditions: 1a (0.2 mmol), base (2.0 equiv) and reaction were irradiated by 30 W blue LEDs at room temperature, stirring for 20 h under air atmosphere. b Isolated yields of 3aa. c DBU (1.0 equiv). d DBU (3.0 equiv). e DBU (4.0 equiv). f The reaction was carried out in the dark. g The reaction was proceeded on 6 mmol scale.
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Wang, L.; Zhang, Q.; Sang, X.; Ding, Q. Photocatalytic Synthesis of 6-Phosphorylated Phenanthridines from 2-Isocyanobiphenyls via Radical C−P and C−C Bond Formation. Catalysts 2023, 13, 1036. https://doi.org/10.3390/catal13071036

AMA Style

Wang L, Zhang Q, Sang X, Ding Q. Photocatalytic Synthesis of 6-Phosphorylated Phenanthridines from 2-Isocyanobiphenyls via Radical C−P and C−C Bond Formation. Catalysts. 2023; 13(7):1036. https://doi.org/10.3390/catal13071036

Chicago/Turabian Style

Wang, Liping, Qin Zhang, Xiaoyan Sang, and Qiuping Ding. 2023. "Photocatalytic Synthesis of 6-Phosphorylated Phenanthridines from 2-Isocyanobiphenyls via Radical C−P and C−C Bond Formation" Catalysts 13, no. 7: 1036. https://doi.org/10.3390/catal13071036

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