Synthesis of 2H-Thiopyrans by Rhodium(II) Acetate-Catalyzed Reaction of 4-Amino-2,5-dihydro-3-thiophenecarbonitriles with a-Diazocarbonyl Compounds II [1]

Summary.

 The reaction of 4-amino-2,5-dihydro-2- and -5-methyl-3-thiophenecarbonitriles with α-diazocarbonyl compounds in the presence of rhodium(II) acetate gave regioselectively 4-cyano-2H-thiopyrans (C₂-S insertion) in moderate to good yields; 5-cyano-2H-thiopyrans (C₅-S insertion) were not isolated. The starting compounds were synthesized by reaction of tetrahydro-2- and -5-methyl-4-oxo-3-thiophenecarbonitriles with morpholine, piperidine, and pyrrolidine in the presence of formic acid in ethanol.