Bis(NHC) ligand precursors,
L1, based on
trans-1,2-diaminocyclohexane were designed and synthesized. To introduce chirality at the hydroxyamide side arm on the NHC of
L1, a chiral
β-amino alcohol, such as enantiopure leucinol, was used. Cu-catalyzed asymmetric conjugate addition reactions
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Bis(NHC) ligand precursors,
L1, based on
trans-1,2-diaminocyclohexane were designed and synthesized. To introduce chirality at the hydroxyamide side arm on the NHC of
L1, a chiral
β-amino alcohol, such as enantiopure leucinol, was used. Cu-catalyzed asymmetric conjugate addition reactions of cyclic and acyclic enones with Et
2Zn were selected to evaluate the performance of
L1 as a chiral ligand. For the reaction of cyclic enone, a combination of [bis(trimethylsilyl)acetylene]-(hexafluoroacetylacetonato)copper(I) (Cu(hfacac)(btmsa)) with a (±)-
trans-1,2-cyclohexanediamine-based bis(NHC) ligand precursor, (
rac;
S,
S)-
L1, which was prepared from (
S)-leucinol, was the most effective. Thus, treating 2-cyclohexen-1-one (
3) with Et
2Zn in the presence of catalytic amounts of Cu(hfacac)(btmsa) and (
rac;
S,
S)-
L1 afforded (
R)-3-ethylcyclohexanone ((
R)-
4) with 97%
ee. Similarly, use of (
rac;
R,
R)-
L1, which was prepared from (
R)-leucinol, produced (
S)-
4 with 97%
ee. Conversely, for the asymmetric 1,4-addition reaction of the acyclic enone, optically pure (−)-
trans-1,2-cyclohexanediamine-based bis(NHC) ligand precursor, (
R,
R;
S,
S)-
L1, worked efficiently. For example, 3-nonen-2-one (
5) was reacted with Et
2Zn using the CuOAc/(
R,
R;
S,
S)-
L1 catalytic system to afford (
R)-4-ethylnonan-2-one ((
R)-
6) with 90%
ee. Furthermore, initially changing the counterion of the Cu precatalyst between an OAc and a ClO
4 ligand on the metal reversed the facial selectivity of the approach of the substrates. Thus, the conjugate addition reaction of
5 with Et
2Zn using the Cu(ClO
4)
2/(
R,
R;
S,
S)-
L1 catalytic system, afforded (
S)-
6 with 75%
ee.
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