Cyclopropa-Fused Quinones. The Generation and Trapping of Bicyclo[4.1.0]hepta-1(6),3-diene-2,5-dione and 1H-Cyclopropa[b]naphthalene-2,7 dione

The title compounds (3) and (4) have been generated at low temperature by debromosilylation of 1-bromo-6-trimethylsilylbicyclo [4.1.0]hept-3-ene-2,5-dione (23) and 1a-bromo-7a-trimethylsilyl-1a,7a-dihydro-1H-cyclopropa[b]naphthalene-2,7-dione (38) respectively. Both cyclopropa-fused quinones are reactive but each could be trapped with furan to give a pair of cycloadducts, which were remarkably resistant to cycloreversion. In the absence of added trapping agent, the cyclopropanaphthoquinone (4) was intercepted by fluoride ion to give 1a-fluoro-1a,7a-dihydro-1H-cyclopropa[b]naphthalene-2,7-dione (39) in low yield. These findings indicate that the quinones (3) and (4) do not behave like cycloproparenes but still possess much of the reactivity inherent in the strained bicyclo[4.1.0]hept-1(6)-ene system (32). Theoretical calculations at the Becke3LYP/6-31G* level have been carried out on (3) and the isomeric structures bicyclo[4.1.0]hepta-1,5-diene-3,4-dione (1) and bicyclo[4.1.0]hepta-1(6),4-diene-2,3-dione (2); these reveal that (2) and (3) lie 78.7 and 58.6 kJ/mol respectively above (1).