Acid-catalyzed photoreaction of 6-chloro-1,3-dimethyluracil and mesitylene: Formation of photocycloadducts and their characterization

In contrast to the previously reported short time required (1 h) for photol ysis of 6-chloro-1,3-dimethyluracil (6-CIDMU) and mesitylene, in the presen ce of TFA, resulting in two major products: 1,3,6,8, 10-pentamethylcyctooct apyrimidine derivative (1d), and diazapentacyclo[6.4.0.0(1,3).0(2,5).0(4,8) ] dodecane (2c), prolonged irradiation (18h) of this same mixture yields no vel pentalenopyrimidine derivatives, including diazapentacyclo[6.4.0.0(1,3) .0(2,6).0(4,8)] dodecane (3c).