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Stereochemistry Control in the Lewis Acid Mediated Lactonization Reaction of γ,δ‐Epoxy‐β‐silyloxy Esters
Author(s) -
Nacro Kassoum,
Gorrichon Liliane,
Escudier JeanMarc,
Baltas Michel
Publication year - 2001
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200111)2001:22<4247::aid-ejoc4247>3.0.co;2-w
Subject(s) - chemistry , regioselectivity , oxocarbenium , epoxide , ring (chemistry) , stereochemistry , epoxy , lactone , lewis acids and bases , alkoxy group , ring size , carbon 13 nmr , organic chemistry , catalysis , nucleophile , alkyl
ZnCl 2 ‐triggered lactonization reactions of γ,δ‐epoxy‐β‐silyloxy esters with remote alkoxy groups (CH 2 ) n OR ( n = 2, 3), producing five‐ and/or six‐membered ring lactones, have been investigated. Under such conditions, the regiochemistry of the reaction is governed by the cis or trans nature of the starting epoxy ester and also by its C(3) stereochemistry. An X‐ray crystallographic structure of a γ‐lactone (compound 24′ ) and a 13 C NMR correlation for the C(4) carbon chemical shifts of all γ‐lactones were obtained and used to determine the regioselectivity of the epoxide ring‐opening. A mechanistic hypothesis, involving an oxocarbenium ion as a common intermediate, is presented in interpretation of the results.