Small-Ring Compounds. XV. Methylenecyclobutene and Related Substances

Methylenecyclobutene has been synthesized from diethyl methylenemalonate by way of 3-methylenecyclobutanecarboxylic acid and 3-rnethylenecyclobutylamine. The synthesis featured the use of anthracene as a blocking group for the exocyclic double bond during malonic-ester closure of the cyclobutane ring. 4,4-Dimethyl-3-methylenecyclobutene has been obtained by degradation of α-pinene and 1-phenyl-3-methylenecyclobutene by condensation of allene with phenylacetylene. Bromine addition and three types of polymerization of methylenecyclobutene have been found to proceed in accordance with predictions based on simple molecular-orbital theory. 3-Methylenetrimethylene oxide, of interest because of the possibility that it might have demonstrable π-bonding across the ring, has been prepared.