Pyrimidine derivatives and related compounds. Part XXVI. Oxidative and non-oxidative photocyclisations of 5-and 6-phenylthio- and anilino-1,3-dimethyluracils to benzothienopyrimidines and pyrimidoindoles

Abstract

Oxidative photocyclisation of the uracil derivatives (I) and (II), having an N-methylanilino-, a phenylthio-, or an anilino-group at the 5- or the 6-position, gives the corresponding benzothienopyrimidines (IIIa) and (IVa) and the pyrimidoindoles (IIIb and c) and (IVb). Under non-oxidative conditions, irradiation of 5-(N-methylanilino)- and 5-(N-acetylanilino)-1,3-dimethyluracil [(Ib) and (X)] gives the trans-dihydropyrimido[5,4-b]indoles (IX) and (XI) in high yields. The trans stereochemistry and the mechanism of formation of these dihydro-compounds are explained in terms of orbital symmetry arguments and deuterium labelling results.