Silica-supported pyrrolidine–triazole, an insoluble, recyclable organocatalyst for the enantioselective Michael addition of ketones to nitroalkenes

A highly efficient, silica-supported organocatalyst for the Michael addition of ketones to nitroalkenes is successfully developed. A 1,2,3-triazole ring, constructed via a click 1,3-dipolar cycloaddition, plays a dual role of grafting the chiral pyrrolidine onto the silica surface and of providing a structural element complementary to the pyrrolidine. The supported catalyst demonstrated high activity and enantioselectivity; furthermore, it can be readily reused four times without significant loss of catalytic activity.

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(S)-2-((R)-2-Nitro-1-phenylethyl)cyclohexanoneC14H17NO3Ee = 91%[α]D20=-26.1 (c 1.0, CHCl3)Absolute configuration: (S,R)

(S)-2-((R)-1-(2,4-Dichlorophenyl)-2-nitroethyl)cyclohexanoneC14H15Cl2NO3Ee = 88%[α]D20=-43.9 (c 1.0, CHCl3)Absolute configuration: (S,R)

(S)-2-((R)-2-Nitro-1-(3-nitrophenyl)ethyl)cyclohexanoneC14H16N2O5Ee = 87%[α]D20=-23.7 (c 1.0, CHCl3)Absolute configuration: (S,R)

(S)-2-((R)-1-(4-Methoxyphenyl)-2-nitroethyl)cyclohexanoneC15H19NO4Ee = 84%[α]D20=-25.3 (c 1.0, CHCl3)Absolute configuration: (S,R)

(S)-2-((R)-1-(2-Chlorophenyl)-2-nitroethyl)cyclohexanoneC14H16ClNO3Ee = 89%[α]D20=-23.1 (c 1.0, CHCl3)Absolute configuration: (S,R)

(S)-2-((R)-1-(4-Chlorophenyl)-2-nitroethyl)cyclohexanoneC14H16ClNO3Ee = 93%[α]D20=-33.7 (c 1.0, CHCl3)Absolute configuration: (S,R)

(S)-2-((R)-1-(4-Methylphenyl)-2-nitroethyl)cyclohexanoneC15H19NO3Ee = 85%[α]D20=-21.2 (c 1.0, CHCl3)Absolute configuration: (S,R)

(S)-2-((R)-1-(2-Bromophenyl)-2-nitroethyl)cyclohexanoneC14H16BrNO3Ee = 87%[α]D20=-47.9 (c 1.60, CHCl3)Absolute configuration: (S,R)

(S)-2-((R)-1-(4-Bromophenyl)-2-nitroethyl)cyclohexanoneC14H16BrNO3Ee = 89%[α]D20=-25.8 (c 1.0, CHCl3)Absolute configuration: (S,R)

(S)-2-((S)-1-(Furan-2-yl)-2-nitroethyl)cyclohexanoneC12H15NO4Ee = 88%[α]D20=-13.3 (c 1.0, CHCl3)Absolute configuration: (S,S)

(S)-2-((R)-1-(Naphthalen-2-yl)-2-nitroethyl)cyclohexanoneC18H19NO3Ee = 77%[α]D20=-28.5 (c 1.0, CHCl3)Absolute configuration: (S,R)

(R)-5-Nitro-4-phenylpentan-2-oneC11H13NO3Ee = 40%[α]D20=-7.2 (c 1.0, CHCl3)Absolute configuration: (R)