Cage Enlargement of 1,4-Bis(hydroxymethyl)pentacyclo(4.2.0.02,5.03,8.04,7)octane to a Tetracyclo(4.3.0.03,9.04,7)nonane System in Formic Acid.

Cationic rearrangement of 1,4-bis(diarylhydroxymethyl)pentacyclo[4.2.0.02,5.03,8.04,7]octanes (1) in formic acid gave new cage compounds, 8,8-diaryl-2-diarylmethylene-exo-5-(formyloxy)tetracyclo[4.3.0.03,9.04,7]nonan-7-ols (3) and new cage-degradation products, 5,5-diaryl-4-[4-(diarylmethylene)-2-cyclobutenyl]-2-cyclopenten-1-ones (4) along with Wagner–Meerwein rearrangement products, pentacyclo[5.3.0.02,5.03,9.04,8]decanes (5; C2-bishomocubanes) and pentacyclo[5.3.0.02,6.03,9.04,8]decanes (6; D2h-bishomocubanes). 9,9-Diaryl-4-(diarylhydroxymethyl)pentacyclo[4.3.0.02,5.03,8.04,7]nonan-1-ols (2) gave 4, 5, and 6 without the formation of 3. A Wagner–Meerwein 1,2-bond shift of 1 gave key intermediates 2 which were converted into 3 via homoallylic rearrangement, into 4 via pinacol–pinacolone-like rearrangement, or into 5 and 6 via Wagner–Meerwein rearrangement.