Acid-catalyzed photoreaction of 6-chloro-1,3-dimethyluracil in frozen benzene: Formation of novel cycloadducts, tetrahydropentaleno[1,2-e]pyrimidine-2,4-dione derivatives

Contrasting to the photoreaction of 6-chloro-1,3-dimethyluracil in benzene at ambient temperature in the presence of trifluoroacetic acid, whereby 1,3-dimethylcyclooctapyrimidine was produced as a sole cycloadduct, the similar photoreaction in frozen benzene at -15 similar to -20 degrees C proceeded quite differently to give three novel photocycloadducts, 7-chloro-1,3-dimethyl-4b,5,7a,8-tetrahydropentaleno[1,2-e]pyrimidine-2,4-dione, 5-chloro-1,3-dimethyl-4b,7,7a,8-tetrahydropentaleno[ 1,2-e]pyrimidine-2,4-dione, and 6-chloro-10,12-diazapentacyclo[6.4.0.0(1,3).0(2,5).0(4,8)]-dodecane-9,11-dione.