MOLECULAR-STRUCTURES AND PHOTOCHEMICAL BEHAVIOR OF DOUBLY BRIDGED PRISMANES

The molecular structures of four prismanes were determined by X-ray an alysis. The diester derivatives 1a, 1b, and 3 show a lengthening of th e vicinal bonds and a shortening of the distal bonds in the cyclopropa ne moieties, whereas in bis(hydroxymethyl) compound 2 no significant b ond length differences were found. These structural properties affect their chemical behavior: if prismanes la and Tb are irradiated with UV light a selective cleavage of the elongated cyclopropane bonds afford s exclusively Dewar benzenes 4a and 4b as primary products whereas fro m 2 both possible isomeric Dewar benzenes 8 and 9 are obtained.