1-Cyclohexene- 1,2-dicarboxylic anhydride (I) reacts with butadiene, isoprene, and dimethylbutadiene only under vigorous conditions (12 hours at 175 "C) to give 50-60% yields of thermal [2 + 41 adducts.'r2 It does not react even at 175 "C with furan, chloroprene, or cyclopentadiene.2 We have found that, in contrast to its reluctance to undergo thermal cycloaddition, I reacts readily with a variety of olefins under irradiation with weak ultraviolet light at 25-80 "C to give [2 + ...
