Enaminones as building blocks in heterocyclic synthesis: New syntheses of nicotinic acid and thienopyridine derivatives

Reacting 1,3-diphenyl-propan-2-one with equimolecular amount of dimethylformamide dimethylacetal afforded the enaminone 4. This when reacted with another equimolecular amount of dimethylformamide dimethylacetal afforded the dienaminone 5. Compound 4 condenses with cyanothioacetamide and with cyanoacetamide to yield 2-thioxo- and 2-oxo-pyridine-3-carbonitrile derivatives 6a,b respectively. Compound 6a reacted with cc-chloroacetone 8 to yield the thieno[2,3-b]pyridine derivative 10 that cyclized further into 4,7,8-trisubstituted pyrido[2',3':2,3] thieno[4,5-d]pyrimidine 12. Compound 4 also afforded 2,5,6-trisubstituted nicotinic acid ethyl ester 13 by reaction with ethyl acetoacetate in acetic acid in the presence of ammonium acetate. The dienaminone 5 reacted with acetic acid, ammonium acetate/acetic acid, phenylhydrazine and 5-amino-3-methylpyrazole yielding 3,5-diphenyl-pyran-4-one 15a, 3,5-diphenyl-1H-pyridin-4-one 15b and 1,3,5-trisubstituted pyridin-4-ones 16a-b.