Regiochemical control in the preparation of 2-(nosyloxy) .beta.,.gamma.-unsaturated esters and 4-(nosyloxy) .alpha.,.beta.-unsaturated esters from 1-[(trimethylsilyl)oxy]-1-alkoxy 1,3-dienes
摘要:
A series of 1-[(trialkylsilyl)oxy]-1-alkoxy 1,3-dienes 1a-i were found to react with p-nitrobenzenesulfonyl peroxide in the presence of sodium methoxide or zinc chloride to give alkyl 2-[[(p-nitrophenyl)sulfonyl]oxy] beta-gamma-unsaturated esters 3 and alkyl 4-[[(p-nitrophenyl)sulfonyl]oxy] alpha,beta-unsaturated esters 4 which are readily separable. The regioselectivity is determined by kinetic versus thermodynamic control. When positions 2 or 4 of the diene are unsubstituted, the 2-isomer is the major product and is the kinetically fastest formed product. It can be thermally rearranged to the more stable 4-isomer. When alkyl substituents are present at either the 2- or 4-positions, only the 4-isomer is obtained. Substitution for nosylate by amine nucleophiles occurs by an S(N)2 process. Thus 2-amino beta,gamma-unsaturated esters and 4-amino alpha,beta-unsaturated esters can be prepared from the appropriate starting nosylate.
Regiochemical control in the preparation of 2-(nosyloxy) .beta.,.gamma.-unsaturated esters and 4-(nosyloxy) .alpha.,.beta.-unsaturated esters from 1-[(trimethylsilyl)oxy]-1-alkoxy 1,3-dienes
摘要:
A series of 1-[(trialkylsilyl)oxy]-1-alkoxy 1,3-dienes 1a-i were found to react with p-nitrobenzenesulfonyl peroxide in the presence of sodium methoxide or zinc chloride to give alkyl 2-[[(p-nitrophenyl)sulfonyl]oxy] beta-gamma-unsaturated esters 3 and alkyl 4-[[(p-nitrophenyl)sulfonyl]oxy] alpha,beta-unsaturated esters 4 which are readily separable. The regioselectivity is determined by kinetic versus thermodynamic control. When positions 2 or 4 of the diene are unsubstituted, the 2-isomer is the major product and is the kinetically fastest formed product. It can be thermally rearranged to the more stable 4-isomer. When alkyl substituents are present at either the 2- or 4-positions, only the 4-isomer is obtained. Substitution for nosylate by amine nucleophiles occurs by an S(N)2 process. Thus 2-amino beta,gamma-unsaturated esters and 4-amino alpha,beta-unsaturated esters can be prepared from the appropriate starting nosylate.
Nucleophilic Displacement Reactions of 4-(Nosyloxy)-2,3- unsaturated Esters and 2-(Nosyloxy)-3,4-unsaturated Esters
作者:Robert V. Hoffman、Bryon S. Severns
DOI:10.1021/jo960477m
日期:1996.1.1
It has been found that 4-(nosyloxy)-2,3-unsaturated esters 2 undergo direct displacement with a wide variety of nucleophiles and yield 4-substituted-2,3-unsaturated products cleanly and in generally good yields. These materials thus have very good synthetic potential for the formation of densely functionalized unsaturated esters. 2-(Nosyloxy)-3,4-unsaturated esters as exemplified by methyl 2-(nosyloxy)-3-butenoate (3d) also undergo direct displacement with a range of good nucleophiles; however, the resulting substitution products are prone to rearrangements and tautomerism, as is the starting material itself, so that the synthetic utility of these compounds is limited.
HOFFMAN, ROBERT V.;KIM, HWA-OK, J. ORG. CHEM., 56,(1991) N, C. 1014-1019