AB-INITIO THEORETICAL INVESTIGATION ON THE WRIGHT-WEST AND WITTIG ANIONIC MIGRATION REACTIONS

被引:23
作者
ANTONIOTTI, P
TONACHINI, G
机构
[1] UNIV TURIN, IST CHIM ORGAN, VIA PIETRO GIURIA 7, I-10125 TURIN, ITALY
[2] UNIV TURIN, DIPARTIMENTO CHIM GEN & ORGAN APPLICATA, I-10125 TURIN, ITALY
关键词
D O I
10.1021/jo00066a011
中图分类号
O62 [有机化学];
学科分类号
070303 ; 081704 ;
摘要
The carbanion to oxyanion rearrangements in the (H2COSiH3)- and (H2COCH3)- model systems have been studied. In the case of silicon the direct [1,2] migration takes place in two steps with low energy barriers, passing through a cyclic intermediate species in which silicon is pentacoordinate. In contrast, the model carbon [1,2] migration goes through a single transition structure and, although very exothermic, presents a significantly higher energy barrier. An estimate of the energy barriers for methyl and silyl dissociation shows that the former is preferred over a methyl [1,2] shift, while the latter is much more difficult than silyl [1,2] migration. The remarkable differences between the two reaction energy profiles lie in the stability of the silicon cyclic intermediate. The significant strain introduced as a result of pentacoordination within a cyclic structure is overcome by the ability of the silyl group as a whole to delocalize to some extent the negative charge of the system through bonding interactions with the H2CO group.
引用
收藏
页码:3622 / 3632
页数:11
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