Synthesis of 2,3,4,6-tetrasubstituted pyridines as precursors to Bicycles and polycycles

Ammonium 1,1,3-tricyano-2-methylprop-2-enide 1a and sodium 2-amino-1,1,3-tr icyanoprop-2-enide 1b are treated with H2S in absolute ethanol to afford 3, 4,6-trisubstituted pyridine-2(1H)-thione 3a,b; their structures are confirm ed by reaction with phenacyl bromide to give 4a,b; also 3a,b reacts with DM FDMA to give 6a,b, and on treatment of 6a with phenacyl bromide affords 8; reaction of 4b with DMFDMA gave 9 while methylation of 3a,b by methyl iodid e in ethanolic sodium hydroxide gives 10a,b.