WAGNER-MEERWEIN REARRANGEMENT OF 4-HYDROXYMETHYLPENTACYCLO[4.3.0.0(2,5).0(3,8).0(4,7)]NONANE TO PENTACYCLO[5.3.0.0(2,6).0(3,9).0(4,8)]DECANE IN FORMIC-ACID

The cationic rearrangement of 1-bromo-4-[hydroxybis(4-methoxyphenyl)methyl]pentacyclo[4.3.0.0(2,5).0(3,8). 0(4,7)]nonane-9-spiro-2'-[1,3]dioxolane (1) in formic acid gave 4-bromo-1-formyloxy-10,10-bis(4-methoxy-phenyl)pentacyclo[5.3.0.0(2,6).0(3,9).0(4,8)]decane-5-spiro-2'-[1,3]dioxolane in 27%, yield along with 5-bromo-9-formyloxy-10,10-bis(4-methoxyphenyl)pentacyclo[5.3.0.0(2,5).0(3,9).0(4,8)]decane-6-spiro-2'-[1,3]dioxolane in 55% yield. The reaction of 1 with p-toluenesulfonic acid or hydrochloric acid in methanol also afforded 4-bromo-1-methoxy-10,10-bis(4-methoxyphenyl)pentacyclo[5.3.0.0(2,6).0(3,9)0(4,8)]decane-5-spiro-2'-[1,3]dioxolane together with 5-bromo-9-methoxy-10,10-bis(4-methoxyphenyl)pentacyclo[5.3.0.0(2,5).0(3,9).0(4,8)]decane-6-spiro-2'-[1,3]dioxolane. With respect to migration of the C4-C5 bond in the pentacyclo[4.3.0.0(2,5).0(3,8).0(4,7)]nonane (homocubane) skeleton to pentacyclo[5.3.0.0(2,6).0(3,9).0(4, 8)]decane (D2h-bishmocubane), a rearrangement into the bishomocubane system in driven by a concomitant release of strain; also, the stability of the 4-homocubane-methyl cation intermediate may play an important role in determining the course of the cage expansion into the D2h-bishomocubane system. This reaction provides an attractive route for the synthesis of bishomocubane bridgehead alcohols and related compounds which are not easily accessible by other routes.