| An approach is described for the stereospecific conversion of threo and erythro 1,2-eopxy-3-alkanols to cis and trans internal epoxides, respectively, via an alkylative rearrangement of the corresponding p-toluenesulphonate esters. This rearrangement may be used to prepare both cis and trans disubstituted epoxides in high optical purity and in good yield. Indeed, using this new method, we have prepared both enantiomers of (Z,Z)-2(2,5-octadienyl)-3-undecyloxirane, a sex pheromone component of several Arctiid moths.;From the results obtained, it is clear that this approach is complementary to existing methods for the stereoselective synthesis of epoxides, such as the Payne rearrangement and asymmetric epoxidation.;Chapter 2 outlines the development of two methods for the regioselective conversion of epoxides to vicinal bromo- and chlorohydrins using B-bromobis(dimethylamino)borane (BDB) and dilithium tetrachlorocuprate (Li;Reaction of BDB with 1-alkene oxides afforded 1-bromo-2-alkanols, while the more substituted bromides predominated in bromohydrin mixtures derived from stryene oxide and 1-methylcyclohexene oxide. Analogously, Li... |
