Rearrangement of epoxides. Part I. Preparation and rearrangement of the α- and β-epoxides of 14,15-bisnorlabd-8-en-13(R and S)-yl acetates and of related epoxides

Abstract

The preparation and rearrangement with boron trifluoride–ether complex of a number of 8α,9α- and 8β,9β-epoxy-14,15-bisnor- and 14,15,16-trisnor-labdane derivatives have been carried out to determine whether the clerodane diterpene skeleton could be obtained. A variety of rearranged carbon skeletons has been obtained but not that of clerodane, probably because formation of this would involve the generation of a 1,3-diaxial interaction between the the methyl groups at C-5 and C-9.

In an attempt to modify the course of the rearrangements in these epoxy-decalin derivatives, the α- and β-epoxides have been prepared from 6β-hydroxy-1,2,5,5,9β-pentamethyl-Δ¹-octalin and 6β-hydroxy-1,5,5,9β-tetramethyl-Δ¹-octalin and their rearrangements studied. The results are best explained by assuming that the epoxides rearrange in a non-concerted manner even when the migrating groups are antiperiplanar and that the key factor determining the products is the nature of the steric interactions in the starting epoxide and in the products.

A novel product from the bisnorlabdane epoxide (14) is the cyclodecenone (42).