Synthesis of 1,4-Oxathiocines and Thiopyrans by the Reaction of 2- Amino-4,5-dihydro-3-thiophenecarbonitriles with Ethyl Diazoacetoacetate.

The reaction of 4,5-dihydro-2-(4-morpholinyl)- or -2-(1-piperidinyl)- or -2-(1-pyrrolidinyl)-3-thiophenecarbonitriles 1a–i with ethyl diazoacetoacetate in the presence of rhodium (II) acetate dimer gave the corresponding ethyl 1,4-oxathiocine-3-carboxylates 2a–f, h and acetyl(dihydro-1-thiophenylio)-(ethoxycarbonyl)methanides 3a, b. Compounds 2a–f, h and 3a, b were heated at 140°C to give the corresponding ethyl thiopyran-6-carboxylates 4a–i in moderate to good yields.