Stereoselective radical additions of γ-oxy-α,β-unsaturated ester derivatives; 1,2-asymmetric induction in acyclic and cyclisation systems
摘要:
Examination was made of 1,2-asymmetric induction in the addition of alkyl radicals to gamma-oxy-alpha,beta-unsaturated ester derivatives 1 and 2 prepared from ethyl lactate and (R)-2,3-0-isopropylideneglyceraldehyde 3, respectively. The addition reactions of hexyl, cyclohexyl and 3-phenylpropyl radicals to (Z)-2 derived from aldehyde 3 gave beta-addition products with syn-stereoselectivity (syn:anti = 8.6:1-syn only). The reactions of (E)-2 were non-stereoselective. Based on allylic strain, a transition-state model for the syn-stereoselectivity is proposed. 1,2-Asymmetric induction was carried out in radical cyclisation to synthesize optically active cyclohexane derivatives.
Stereoselective radical additions of γ-oxy-α,β-unsaturated ester derivatives; 1,2-asymmetric induction in acyclic and cyclisation systems
摘要:
Examination was made of 1,2-asymmetric induction in the addition of alkyl radicals to gamma-oxy-alpha,beta-unsaturated ester derivatives 1 and 2 prepared from ethyl lactate and (R)-2,3-0-isopropylideneglyceraldehyde 3, respectively. The addition reactions of hexyl, cyclohexyl and 3-phenylpropyl radicals to (Z)-2 derived from aldehyde 3 gave beta-addition products with syn-stereoselectivity (syn:anti = 8.6:1-syn only). The reactions of (E)-2 were non-stereoselective. Based on allylic strain, a transition-state model for the syn-stereoselectivity is proposed. 1,2-Asymmetric induction was carried out in radical cyclisation to synthesize optically active cyclohexane derivatives.
One-Pot Preparation of Ethyl 2(Z)-4-(Anilinoxy)pentenoate by α-Aminoxylation of Propanal Followed by Z-Selective HWE Reaction and the Study on Its Cyclization Reaction
作者:Kaori Ando、Mami Takao、Ikumi Oyama、Kouki Furuta
DOI:10.3987/com-18-13932
日期:——
A one-pot sequence of alpha-aminoxylation of n-propanal catalyzed by L-proline followed by the Z-selective Horner-Wadsworth-Emmons reaction was developed. The highly functionalized chiral gamma-anilinoxy-Z-alpha,beta-unsaturated ester 6 was obtained in 57-58% yield with 98:2 Z-selectivity from n-propanal in one-pot procedure. The transformation of the anilinoxy group of 6 into a hydroxyl group can be carried out by treatment with catalytic amount of CuSO4 in methanol to give either the corresponding alcohol 8 or chiral gamma-valerolactone 4a in moderate yield. Chiral 6-methyl-2-phenyl-2H-1,2-oxazin-3(6H)-one 7 was obtained in 75% yield from 6 by treatment with CSA.
Stereoselective radical additions of γ-oxy-α,β-unsaturated ester derivatives; 1,2-asymmetric induction in acyclic and cyclisation systems
Examination was made of 1,2-asymmetric induction in the addition of alkyl radicals to gamma-oxy-alpha,beta-unsaturated ester derivatives 1 and 2 prepared from ethyl lactate and (R)-2,3-0-isopropylideneglyceraldehyde 3, respectively. The addition reactions of hexyl, cyclohexyl and 3-phenylpropyl radicals to (Z)-2 derived from aldehyde 3 gave beta-addition products with syn-stereoselectivity (syn:anti = 8.6:1-syn only). The reactions of (E)-2 were non-stereoselective. Based on allylic strain, a transition-state model for the syn-stereoselectivity is proposed. 1,2-Asymmetric induction was carried out in radical cyclisation to synthesize optically active cyclohexane derivatives.