ALPHA-ALPHA-DIOXOKETENE DITHIOACETALS AS STARTING MATERIALS FOR THE SYNTHESIS OF POLYSUBSTITUTED PYRIDINES

Reactions of 3-acetyl-4,4-bis(methylthio)but-3-en-2-one 2e and methyl 2-acetyl-3,3-bis (methylthio)prop-2-enoate 2f with cyanothioacetamide, cyanoacetamide, or 2-amino-1,3,3-tricyanoprop-1-ene and base, followed by treatment with acid, give polysubstituted pyridines such as 8, 10, 11, 13, 15 and 16. Further elaboration of these products leads to bicyclic systems such as thieno[2.3-b] pyridines 17 and 18 and pyrazolo[3,4-c] pyridine 21 and then to tricyclic systems including pyrazolo[3.4-d]thieno[2,3-b]pyridine 19 and dipyrazolo[3,4-b:3',4'-6]pyridine 22.