Tandem radical mediated 5-exo-trig, 6-endo-dig cyclization. Stereoselectivity, alpha-trimethylsilyl effect and the product spread .4

Stereochemistry and mechanism of the title reaction have been investigated. The reaction proceeds well in the (S) series. In the epimeric (R) series a product spread is usually observed. In either series olefin configuration is lost (7 examples), consistent with a freely rotating exocyclic radical i...

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Bibliographic Details
Published inTetrahedron Vol. 53; no. 25; pp. 8401 - 8420
Main Authors Breithor, M, Herden, U, Hoffmann, HMR
Format Journal Article
LanguageEnglish
Published OXFORD Elsevier 23.06.1997
Subjects
Chemistry
Chemistry, Organic
Physical Sciences
Science & Technology
(+/-)-HIRSUTENE
ETHERS
KINETIC RESOLUTION
INITIATED POLYOLEFINIC CYCLIZATIONS
MODEL
EPOXIDATION
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Summary:Stereochemistry and mechanism of the title reaction have been investigated. The reaction proceeds well in the (S) series. In the epimeric (R) series a product spread is usually observed. In either series olefin configuration is lost (7 examples), consistent with a freely rotating exocyclic radical intermediate. An alpha-trimethylsilyl group at the olefinic terminus enhances the selectivity of the radical cascade Spectroscopic evidence and MMX calculations suggest that the tandem annulation products of the (S) series are favoured thermodynamically, being more stable than those of the (R) series. Pyranoside (R)G2a is frozen in a half chair conformation. (C) 1997 Elsevier Science Ltd.
ISSN:0040-4020
DOI:10.1016/S0040-4020(97)00519-X