Pyridine Syntheses. II. Condensation Routes Toward Streptonigrin Ring C [1]

Article abstract of DOI:10.1002/jhet.5570350113

Alternative complimentary syntheses of penta-substituted pyridine rings with full regiochemical control of substituents were studied as a method for the synthesis of Streptonigrin (1). Various α-substituted acetophenones 2 were reacted with enones 3 in acetic acid/ammonium acetate and air to afford penta-substituted pyridines 4. α-Substituents that could provide a source of exocyclic nitrogen at position 3 of these Steptonigrin ring-C models proved to be the limiting factor. However, an inverse "3+2+1" cyclocondensation of α-cyanochalcone 5c with 2-furyl ethyl ketone (6b) afforded the desired model 6-(2-furyl)-5-methyl-2,4-diphenyl-3-pyridinecarbonitrile (4g) in 75% yield.