Recent Advances of Dicyanopyrazine (DPZ) in Photoredox Catalysis

Round 1

Reviewer 1 Report

This review deals with the synthesis, electronic features, redox reactions and their reaction mechanisms of dicyanopyrazine (DPZ). Since DPZ is a photoredox catalyst that has been receiving a lot of attention recently, this review is expected to attract the attention of readers. I judge that this review can be accepted if the following points are revised.

(1) In page 4, Scheme 2, the structure of product 7 is incorrect. One nitrogen is lost.

(2) In page 4, Scheme 2, I don't know what the expression "•••" means. I think it is better to change it to "<1" or "0".

(3) In page 4, lines 97-98. The authors need to enhance completely the description of Scheme 3.

(4) In page 4, line 104, and in page 5, caption of Scheme 4. Do you need alpha ? If the authors think it is necessary, why not specify it in the structure of compound 11 ?

(5) In page 5, Scheme 4,  "'Ar" on compound 9 is recommended to revise to "Ar'".

(6) In page 5, Scheme 5. The font of the left edge is different from the others.

(7) In page 6, Scheme 6, the font below the arrow in the figure above is different from the others.

(8) In page 8, reference 29. 2021 is correct instead of 2020.

Author Response

1. In page 4, Scheme 2, the structure of product 7 has been corrected.
2. In page 4, Scheme 2, the expression "•••" has been changed to "<1" .
3. In page 4, lines 97-98, the description of Scheme 3 has been incorporated.
4. In page 4, line 104, and in page 5, alpha has been also specified in the structure of compound 11.
5. In page 5, Scheme 4,  "'Ar" on compound 9 has been revised to "Ar'".
6. In page 5, Scheme 5, the font of the left edge has been corrected.
7. In page 6, Scheme 6, the font below the arrow in the figure above has been modified.
8. In page 8, reference 29 has been corrected.

Reviewer 2 Report

Manuscript ID: photochem-1317241

This review describe the use of dicyanopyrazine (DPZ) derivatives as organic photocatalysts. The structure of these push-pull molecules, including a D-p-A system (donor-p linker-acceptor) allows easy property tuning, though the usually employed as photocatalyst is the one with two 5-methoxythienyl groups at the 5,6 positions of the pyrazine core. The work in this area has been developped almost exclusively by F. Bures and Z. Jiang.

• The organization of the review is deficient, thus it is hardly understandable.
• The contents of Chapter 2. Synthesis of DPZ and Chapter 3. Photochemistry of DPZ, is described exactly in the pages 1092 and 1093 of the minireview of reference 29: Vega-Peñaloza, A.; Mateos, J.; Companyó, X.; Escudero-Casao, M.; Dell’Amico, L. A Rational Approach to Organo-Photocatalysis: Novel Designs and Structure-Property Relationships. Chem. Int. Ed., 2021, 60, 1082-1097.
• In Chapter 4. Applications in photoredox chemistry, The articles [30-44] of the chemical transformations with DPZ as photocatalyst are not described. Only four references [45-48] are showed.  

   

References:

Page 1 line 38.- together with references [18-24] include ref 13.

In reference 25 that includes references of the authors, at least must be removed those corresponding to reviews (25h, 25o, 25p, 25q, 25r)

Reference 26c must be removed because it refers to DOPO-piperazine (compound with N-P bonds) instead of dicyanopyrazine, DPZ

In reference 29 change the year 2020 by 2021.

In references 21 and 44, the authors must be completed.

Complete reference 48 with the title.

Author Response

1. The articles [30-44] of the chemical transformations with DPZ as photocatalyst belongs to same author, which has been already cited in the review.
2. Page 1 line 38, ref 13 has been incorporated together with references [18-24].
3. Reference 26c has been removed.
4. In reference 29 year has been corrected.
5. In references 21 and 44, the author's name has been  completed.
6. Reference 48 has been completed with the title.

Reviewer 3 Report

The manuscript submitted by P. P. Singh and coworkers reports on applications of dicyanopyrazine (DPZ) as photoredox catalyst for organic synthesis.

My first question is the use of the abbreviation DPZ: is this an established abbreviation for the title compound or one proposed by the authors? Neither dicyanopyrazine nor (4,5-disubstituted) pyrazine-2,3-dicarbonitrile should result in DPZ.

The sentences (Introduction, 2^nd paragraph, lines 38 - 40):

• 4,5-disubstituted-pyrazine-2,3-dicarbonitrile (dicyanopyrazine, DPZ) and its derivatives have emerged as outstanding organic photo- redox catalysts for diverse synthetic organic transformations.

And (lines 40 – 41):

• PZ has been reported to display excellent catalytic activity in various chemical transformations.

Both of them tell almost the same, thus one of the two is redundant.

The authors use the abbreviations SET and EnT without explanation. While these abbreviations may be well known inside the narrow area of organic photocatalysis, they should be explained for a broader audience when they are used for the first time.

Line 60 and references: The surname of the author of ref. (26) is Bureš, not Bures or even Buresˇ.

In 2012, F. Buresˇ and co-workers [26] were presented push–pull molecules (…): It should probably read: In 2012, F. Bureš and co-workers [26] presented push–pull molecules (…)

Lines 69 and 72: please explain the meaning of CT and EDGs when using the abbreviations for the first time (albeit they are explained further below, lines 81 and 83).

Lines 142 and 143: (…) its applications in organic transformations is (…) should probably read (…) its applications in organic transformations are (…)

General remark: the paper reads well; the references list is appropriate and up to date. However, I miss (in Introduction as well as in Conclusions) a comparison of DPZ when compared to other visible light organophotoredox catalysts, to justify the claims in the Abstract (… has shown great potential …). Please add some comparison and try to point out some advantages of DPZ over other known photocatalysts.

Author Response

1. Abbreviation DPZ has been proposed by the authors Zhiyong Jiang et.al.
2. In introduction second paragraph (lines 38-40 and 40-41) has been modified as suggested by reviewer.
3. The abbreviations SET and EnT has been incorporated with their full explanation in the manuscript for the first time.
4. The surname of the author of ref. (26) and line 60 has been corrected.
5. In 2012, F. Buresˇ and co-workers [26] were presented push–pull molecules (…) has been has been corrected.
6. The meaning of CT and EDGs using the abbreviations for the first time has been corrected.
7. Lines 142 and 143: (…) its applications in organic transformations is (…) has been corrected. 
8. Comparison of DPZ with other visible light organophotoredox catalysts has been incorporated in the introduction part of manuscript.

Round 2

Reviewer 2 Report

I confirm my first decision.

Author Response

Dear Sir,
In response to your comment the text of section 3 has been rewritten, which is also highlighted in the manuscript. Therefore, it is requested you to consider my revised review entitled “Recent advances of dicyanopyrazine (DPZ) in photoredox catalysis” for publication in your esteemed Journal.