Reaction mechanism studies. 5. The mechanism of the diaxial → diequatorial rearrangement of β-chlorothioethers
作者:
J. F. King,
K. Abikar,
期刊:
Canadian Journal of Chemistry
(NRC Available online 1968)
卷期:
Volume 46,
issue 1
页码: 9-13
ISSN:0008-4042
年代: 1968
DOI:10.1139/v68-002
出版商: NRC Research Press
数据来源: NRC
摘要:
p-Methoxy- andp-nitro substituted analogues (1band1c) of the diaxial β-chlorothioether 2β-chloro-3α-(phenylthio)-5α-cholestane (1a), have been prepared and found to undergo the diaxial → diequatorial rearrangement. The rates of rearrangement of these compounds show the sequencep-methoxy > H >p-nitro. It is concluded that the transition state for the rearrangement is polarized in the sense of a sulfonium chloride (3). The rearrangement of1ais 1600 times faster in butanol than in decalin (at 110°). There is thus no inherent insensitivity to solvent change in a rearrangement in which there may be a "four-atom arrangement" in the transition state, a conclusion relevant to previous work on the diaxial → diequatorial rearrangement of 1,2-dibromides (1). It was further found that the nitro group slowed the rearrangement (at 110°) more in butanol than in decalin, an observation regarded as consistent with, but not requiring, the incursion of a merged ion-pair, cyclic concerted mechanism.
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