RING EXPANSION OF ISOPROPENYLCYCLOPROPANES TO DIHYDROMETHYLOXEPINS

The stereochemistry was studied concerning the ring expansion of some 2-isopropenylcyclopropane-1-carbonyl compounds to 2,5-dihydro-3-methyl oxepin derivatives. The LAH reduction of dimethyl 2-isopropenylcyclopr opane-1,1-dicarboxylate (1aa) gave the corresponding diol, and a subse quent Swern oxidation gave a seven-membered 4,7-dihydro-6-methyloxepin -3-carbaldehyde. A DIBAL reduction of 1aa gave two isomeric hydroxymet hyl carboxylic esters, and a subsequent Swern oxidation of methyl meth yl-t-2-isopropenylcyclopropane-r-1-carboxylate caused a ring expansion to give methyl 4,7-dihydro-6-methyloxepin-3-carboxylate; however, a s imilar Swern oxidation of methyl ethyl-c-2-isopropenyl-cyclopropane-r- 1-carboxylate caused no ring expansion to give methyl ormyl-c-2-isopro penylcyclopropane-r-1-carboxylate.