Catalytic [4+1]-annulation of thioamides with carbenoid precursors

A Rh(II)/Cu(I)-catalyzed [4 + 1]-annulation of readily available thioamides with 1-sulfonyl-1,2,3-triazoles and diazoamides was developed, delivering a general approach toward highly substituted dihydrothiophenes. A series of dihydrothiophenes having a wide diversity of functional groups, including spirocyclic, dispirocyclic and bicyclic derivatives were synthesized in high yields and good diastereoselectivity. The diastereoselectivity for the reaction of 2-(morpholino-4-carbonothioyl)-3-phenylacrylonitrile with diazoacetamides can be switched by replacing Rh(II) with a Cu(I) catalyst. Cycloalkylidene substituted thioamides formed various regioisomers under Rh(II) or Cu(I) catalysis. Furthermore, reactions of 3-diazomethylindolin-2-one with thioamides can be performed enantioselectively with ee up to 97%.