Studies of intramolecular alkylidene carbene reactions; an approach to heterocyclic nucleoside bases

A series of investigations into the applications of intramolecular cyclisations of alkylidene carbenes are described. The insertion reaction of the carbene generated from 1,4-di(tert-butyldimethylsilyloxy)-3-benzyloxy-butane-2-one to the benzylic position proceeded in good yield and a diastereoselectivity of 3.6:1. The corresponding insertion process of 1,4-di(tert-butyldimethylsilyloxy)-3-methyloxymethyl-butane-2-one gave a mixture of products, including one resulting from a competitive trapping of the carbene by the oxygen atom of a silyloxy group.