CONTROL OF REGIOSELECTIVITY IN THE DI-PI-METHANE REARRANGEMENT - TRIPLET-SENSITIZED PHOTOISOMERIZATION OF BENZONORBORNADIENES CARRYING CYANO SUBSTITUENTS IN THE ARYL AND VINYL SEGMENTS

Triplet-sensitized irradiation of 2-cyanobenzonorbornadiene (10) gives rise exclusively to 3-cyanotetracyclo[5.4.0.02,4.03,6]undeca-l(7),8,10-triene (30). This strong preference for benzo-vinyl bridging to C3 has also been observed in the case of the four possible aryl-substituted dicyano derivatives. In all of these examples, striking regiospecificity is exhibited, despite untoward aryl polar effects in two examples. This bonding preference is shown to conform to the vacant orbital energies and shapes present in the starting benzonorbornadienes as calculated by STO-3G procedures and supported by photoelectron spectroscopy. The synthetic approaches to the polar substituted benzonorbornadienes are also detailed. © 1979, American Chemical Society. All rights reserved.