α,α-Dioxoketene dithioacetals as starting materials for the synthesis of polysubstituted pyridines

Abstract

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′-d] pyridine 22.