SYNTHESIS OF DOUBLY BRIDGED PRISMANES - AN INVESTIGATION OF THE PHOTOCHEMICAL BEHAVIOR OF DOUBLY BRIDGED DEWAR BENZENES

Starting from cyclic acetylenes, two stereoisomeric doubly bridged Dewar benzenes of type 14 and 15 were synthesized, and the effects of the chain length and the nature of two other functional groups on their photochemical behavior were examined. The isomers with bridges spanning the 1,4- and 2,3-positions, 14b,c and 25b, reacted to form the respective prismanes, 17b,c and 27b. Isomers 15b-d, with bridges spanning the 1,2- and 3,4-positions, revealed a more complex photochemistry. through consecutive transposition reactions via a total of five intermediates, an unexpected phthalic/terephthalic ester rearrangement was observed. Prismane 38b and Dewar benzenes 39b,c could be characterized directly, and the existence of the other intermediates was deduced indirectly.