EFFECT OF SUBSTITUENTS ON THE COMPETITION BETWEEN SEVERAL MECHANISMS OF NUCLEOPHILIC VINYLIC SUBSTITUTION

被引:11
作者
AMATORE, C
GALLI, C
GENTILI, P
GUARNIERI, A
SCHOTTLAND, E
RAPPOPORT, Z
机构
[1] UNIV ROMA LA SAPIENZA,CNR,CTR MECCANISMI REAZ,DIPARTIMENTO CHIM,I-00185 ROME,ITALY
[2] HEBREW UNIV JERUSALEM,DEPT ORGAN CHEM,IL-91904 JERUSALEM,ISRAEL
[3] ECOLE NORMALE SUPER,DEPT CHIM,CNRS,URA 1679,F-75231 PARIS 05,FRANCE
来源
JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 2 | 1995年 / 12期
关键词
D O I
10.1039/p29950002341
中图分类号
O62 [有机化学];
学科分类号
070303 ; 081704 ;
摘要
In an attempt to encourage vinylic substrates to undertake an S(RN)1-like nucleophilic substitution route, a process that requires acquisition of one electron, a series of stilbene halides bearing one electron-withdrawing substituent on the double bond has been synthesized. Determination of the reduction potential of these substrates confirmed an increased tendency to acquire electrons. However, this effect was so strong that in the reaction of substrates 1-3 with the pinacolone enolate ion under typical S(RN)1 conditions, two consecutive electron-transfer steps occurred, ultimately producing diphenylacetylene 6 without any S(RN)1 products. Evidence was also gathered for a relevant contribution from an ionic halophilic route to the formation of 6. The structurally similar propenal derivative 4 gave instead a novel ionic deformylation process, presumably initiated by a nucleophilic addition of the enolate ion to the aldehydic carbonyl and followed by bromide loss. The fluorenylidene derivative 5 although it has a very favourable redox potential, reacted by an ionic addition-elimination route. Competition by other routes thus hampers the occurrence of the S(RN)1 process and comparison with cases of other vinyl halides analogously undergoing multiple reaction pathways is made.
引用
收藏
页码:2341 / 2350
页数:10
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