S. Yamaguchi et al., RING EXPANSION OF ISOPROPENYLCYCLOPROPANES TO DIHYDROMETHYLOXEPINS, Bulletin of the Chemical Society of Japan, 70(9), 1997, pp. 2215-2219
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.