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.