SYNTHESIS OF DIHYDROTHIOPYRANO[3,4-C]PYRIDINES AND OF FUSION PRODUCTS THEREOF

Reaction of the 6-hydroxy-thiopyrano[3,4-c] pyridine-5-carbonitrile derivative 2 with a-halogeno-carbonyl compounds gave the O-substituted intermediates 3a-d which on treatment with base were converted into the furo[2,3-b]thiopyrano[4,3-d]pyridines 4a-d by fusion of a furan moiety. Cyclization of the corresponding ester 4d led to fusion of a pyrimidine ring, thus yielding the tetracyclic product 8 as well as its N-substituted derivatives 9a-e. Target compounds 2-9 were derived from the three novel heterocyclic parent systems A-C.