✍ Scribed by Anthony J. Burke; W. Ivo O'Sullivan
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Absfmcf: Reaction of aurone epoxideti with a variety of hydroxylic solvents gives rise to a number of diastereomeric solvolysis products. The stereochemistry of these compounds was initially tentatively assigned by comparison of their * H nmr spectra with that of the cryrhro-acetal 15a resulting from acid catalysed methanolysis of the Q-aurone epoxide 2. In this paper we establish the configurations of these solvolysis products on a fumer basii. by obtaining the fhreo ace&l 1Sb by acid catalysed methanolysis of the correspmtding (E)-aurone epoxide 23. Both the eryrhro-1Sa and tbe rhreo-acetal 15b were independently synthesised by an aldol condensation (using LDA as base) of the acetal27 with benxaldehyde, and surprisingly a high level of diastereosclectivity was obtained, which was attributed to secondary orbital interactions between the electrophile and the enolate molecule. When bromomagnesium diisopropylamide (BMDA) was used as the base for this purpose, the product of the selfcondensation of 27 was obtained as a single diastereomer along with the eryfhro-acetal 1Sa and starting material. 0
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