Efficient and stereoselective beta-epoxidation of the 16(17)-double bond of gibberellic acid derivatives with an acylperoxy radical generated by irradiation of alpha-diketones and oxygen

Citation
H. Seto et al., Efficient and stereoselective beta-epoxidation of the 16(17)-double bond of gibberellic acid derivatives with an acylperoxy radical generated by irradiation of alpha-diketones and oxygen, HETEROCYCLE, 54(1), 2001, pp. 81-86
Citations number
19
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Organic Chemistry/Polymer Science
Journal title
HETEROCYCLES
ISSN journal
0385-5414 → ACNP
Volume
54
Issue
1
Year of publication
2001
Pages
81 - 86
Database
ISI
SICI code
0385-5414(20010101)54:1<81:EASBOT>2.0.ZU;2-R
Abstract
Irradiation of gibberellic acid derivatives in the presence of alpha -diket ones in an oxygen saturated solution led to efficient epoxidation of the 16 (17)-double bond to give the 16 beta ,17-epoxides predominantly. The observ ed stereoselectivity of alpha- to beta -epoxidation ranging from 0:100 on 3 ,13-di-O-acetylgibberellic acid methyl ester (7) through 11:89 on its 3,13- di-O-methoxymethyl congener, i.e., beta -selectivity, was in contrast to th e alpha -selectivity of 74:26 resulted from a peracid epoxidation on 7. Thi s clearly illustrates the radical reaction mechanism involving an acylperox y radical as a one-oxygen transfer species, in which the stability of the d iastereomeric transition states of the intermediary alpha -acylperoxy carbo n radical determines the stereochemical course.