CYCLOCONDENSATION OF ALPHA-OXOKETENE DITHIOACETALS WITH BETA-LITHIOAMINO-BETA-SUBSTITUTED ACRYLONITRILES - SYNTHESIS OF 2,6-SUBSTITUTED AND 5,6-ANNELATED 3-CYANO-4-(METHYLTHIO)PYRIDINES

The lithiated β-amino-β-substituted acrylonitriles 4a-d generated in situ by reaction of lithioacetonitrile with either acetonitrile or substituted nitriles undergo cyclocondensation with α-oxoketenedithioacetals through 1,4-addition to afford 2,6-substituted and 5,6-annelated-4-(methylthio)-3-cyanopyridines 6a-m, 11a-h and 12a-b in good yields. A few of the 2,6-diheterylpyridines 6n-q were also synthesized following this procedure. The corresponding α-cinnamoyl 12a-c and α-(5-aryl-2,4-pentadienoyl) (12d) ketenedithioacetals on the other hand underwent cyclization with 4a to afford the corresponding 4-aryl- (or 4-styryl-6-[2-bis (methylthio)ethenyl]-3-cyanopyridines l4a-d in good yields. Raney Nickel desulphurization of some of these pyridines afforded products of reductive dethiomethylation and those formed by reductive alkylation of nitrile group. © 1990.