Wagner-Meerwein Rearrangement of 4-Hydroxymethylpentacyclo2,5.03,8.04,7>nonane to Pentacyclo2,6.03,9.04,8>decane in Formic Acid

Article abstract of DOI:10.1246/bcsj.66.3009

The cationic rearrangement of 1-bromo-4-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-methoxyphenyl)pentacyclo<5.3.0.0 2,6 .0 3,9 .0 4,8 >decane-5-spiro-2'-<1,3>dioxolane in 27percent 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 55percent 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 (D 2h -bishomocubane), a rearrangement into the bishomocubane system is driven by a concomitant release of strain; also, the stability of the 4-homocubanemethyl cation intermediate may play an important role in determining the course of the cage expansion into the D 2h -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.