Applications of a novel carbon-nitrogen bond cleavage reaction (part I). A new synthesis / derivatisation of 5H-indeno[1,2d] pyrimidines and pyrimido[6,1-a]isoindoles.

Abstract

Substituted 6-(4,5-dimethoxy-2-vinylphenyl)-2,4-(1H, 3H) pyrimidinediones (2) undergo ring closure in the presence of a mixture of formic acid and orthophosphoric acid, to give 5H-indeno[1,2-d]pyrimidines (3) and/or pyrimido[6,1-a]isoindoles (4). Cyclization to 3 and/or 4 depends on the nature of substitution in the pyrimidine ring in 2. Electron withdrawing groups at position 4 in 2 favour the formation of the skeleton 3, however, electron donating groups gave more of 4. Compound 2a on acid treatment, gave in addition to 3a, a dimeric product 5. Phosphorus oxychloride treatment of compound 3a generated the 2,4-dichloro compound 7. Two chloro groups behaved differently in their chemical reactivity. When 7 reacted with amines in benzene, generally 2-positional regioisomers predominated, however, in amyl alcohol 2,4-disubstituted amino compounds were formed.