Cyclopropylidene insertion reactions : 2-methoxy-1,2-dimethylbicyclo[1, 1, 0]butane

Abstract

The syntheses of 1,1-dibromo-2-isopropyl-2-methoxy-3,3- dimethylcyclopropane (12), 1,1-dibromo-2-methoxy-2,3,3- trimethylcyclopropane (11), 1,1-dibromo-2-isopropyl-2- methoxycyclopropane (21), 1,1-dibromo-2-methoxy-3,3- dimethylcyclopropane (29) and 1,1-dichloro-2-methoxy-3,3- dimethylcyclopropane (30) are described. The compounds (12), (21) and (29) give rise to alkoxy allenes on treatment with methyllithium in ether. The major product of the reaction of methyllithium with the dibromide (11) is 2-methoxy-1,2-dimethylbicyclo[1,1,0]butane (26). This is the first example of this class of compound. Treatment of the compound (30) with methyllithium in the presence of hexamethylphosphoramide gave the homologous allene, 2-methoxy-4- methylpenta-2,3-diene (25).