Cyclocondensation of α-oxoketene dithioacetals with β-lithioamino-β- substituted acrylonitriles:synthesis of 2,6-substituted and 5,6-annelated 3-cyano-4- (methylthio) pyridines

Abstract

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 14a -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.