CONFORMATIONAL STUDY OF CHIRAL ALKENES - THE INFLUENCE OF PROTECTIVE GROUPS ON THE RELATIVE STABILITY OF GROUND-STATE ROTATIONAL ISOMERS

被引:38
作者
GUNG, BW
WOLF, MA
机构
[1] Department of Chemistry, Miami University, Oxford
关键词
D O I
10.1021/jo00077a023
中图分类号
O62 [有机化学];
学科分类号
070303 ; 081704 ;
摘要
A variable temperature NMR study shows that a protective group on the hydroxy function of a chiral allylic alcohol can either enhance or counter the influence of the vinyl substituent on the ground-state (GS) conformations. If the allylic hydroxy is protected as a methyl ether, the CH-eclipsed form I becomes favored to a greater degree for normal chiral alkenes. Furthermore, conformer I becomes preferred even for the gamma-hydroxy-alpha,beta-unsaturated esters, which normally favor the CO-eclipsed form (II). On the other hand, the tert-butyldimethylsilyl (TBDMS) ether enhances the preference for conformer II for the gamma-hydroxy-alpha,beta-unsaturated esters and diminishes the preference for the CH-eclipsed form of normal chiral alkenes. These facts are explained by the size of the allylic oxygen lone pairs.
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页码:7038 / 7044
页数:7
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