1,3-DIAZAANTHRACENES - PHOTOCHEMICAL [4-PI-PI] CYCLOADDITIONS WITH CYCLOPENTA-1,3-DIENE AND DIMERIZATIONS TO NEW BIS-PYRIMIDINES(4)

Ultra-violet irradiation of 2,4-dichloro-1,3-diazaanthracene 2 or 2,4- dimethoxy-1,3-diazaanthracene 3 with cyclopentadiene yields single [4 pi+4 pi] cycloadducts, which can be transformed into the fused uracil and related pyrimidines by chemical modification of the chlorine or me thoxy substituents; [4 pi+4 pi] head to head anti-dimers 17 and head t o tail anti-dimers 19 are the exclusive products from solution irradia tion of 2 or 3, whereas only anti-dimers 19 are formed in the solid st ate. (C) 1998 Elsevier Science Ltd. All rights reserved.