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Concerted Ring Opening and Cycloaddition of Chiral Epoxy Enolsilanes with Dienes
Author(s) -
Krenske Elizabeth H.,
Lam Sarah,
Ng Jerome P. L.,
Lo Brian,
Lam Sze Kui,
Chiu Pauline,
Houk Kendall N.
Publication year - 2015
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201503003
Subject(s) - cycloaddition , stereocenter , trifluoromethanesulfonate , chemistry , epoxide , enantiomer , stereochemistry , stereospecificity , diene , ring (chemistry) , enantioselective synthesis , medicinal chemistry , organic chemistry , catalysis , natural rubber
Silyl‐triflate‐catalyzed (4+3) cycloadditions of epoxy enolsilanes with dienes provide a mild and chemoselective synthetic route to seven‐membered carbocycles. Epoxy enolsilanes containing a terminal enolsilane and a single stereocenter undergo cycloaddition with almost complete conservation of enantiomeric purity, a finding that argues against the involvement of oxyallyl cation intermediates which have been previously proposed for these types of reactions. Reported are theoretical and experimental investigations of the cycloaddition mechanism. The major enantiomers of the cycloadducts are derived from S N 2‐like reactions of the silylated epoxide with the diene, in which stereospecific ring opening and formation of the two new CC bonds occur in a single step. Calculations predict, and experiments confirm, that the observed small losses of enantiomeric purity are traced to a triflate‐mediated double S N 2 cycloaddition pathway.