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A Novel Stereoselective Reaction Cascade Leading from α ‐Silylated Allylic Alcohols to Aldol‐Type Products
Author(s) -
Fässler Jürg,
Enev Valentin,
Bienz Stefan
Publication year - 1999
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/(sici)1522-2675(19990407)82:4<561::aid-hlca561>3.0.co;2-u
Subject(s) - chemistry , allylic rearrangement , stereocenter , carbocation , moiety , aldol reaction , stereoselectivity , electrophile , stereospecificity , stereochemistry , nucleophile , deprotonation , medicinal chemistry , enantioselective synthesis , organic chemistry , catalysis , ion
The treatment of α ‐silylated allylic alcohols with epoxidizing reagents afforded in a highly stereocontrolled fashion α ‐silylated aldols. The transformation is proposed to proceed either by a reaction cascade involving stereospecific epoxidation of the allylic‐alcohol moiety followed by an acid‐supported pinacol‐type rearrangement, or by a sequence consisting of a π ‐face‐selective electrophilic attack at the allylic silane moiety with hyperconjugative stabilization of the evolving carbocation, followed by rearrangement of the thus obtained pentacoordinated silanium ion (see Scheme 3 ). Depending on the reaction conditions, the π ‐face selectivity of the oxidation step is controlled by the stereogenic C‐atom or the more remote Si‐center of chirality.