There has been considerable work on the synthesis of a-methylene-y-buytrolactones owing to the biological and tumour-inhibiting activities of a number of naturally occurring terpenoids containing this structural unit. 1 More specifically, methylene-tetrahydrofurans have recently received much attention owing to their preformed methylene moiety.' They can readily be synthesized by radical cyclization of (S-bromo- prop-2-ynyl ethers. then oxidized into a-methylene-y-butyro- ...