Synthesis of 1,4‐oxathiocins and 1,3‐oxazines by the reactions of 2‐amino‐4,5‐dihydro‐3‐thiophenecarbonitriles with dibenzoyldiazomethane

The rhodium(II) acetate‐catalyzed reaction of dibenzoyldiazomethane with 4,5‐dihydro‐2‐(4‐morpholinyl)‐ or 2‐(1‐piperidinyl)‐ or 2‐(1‐pyrrolidinyl)‐3‐thiophenecarbonitriles 1 gave the corresponding 4 H ‐1,3‐oxazin‐4‐ones 3 through the cycloaddition of the cyano group of 1 to benzoylphenylketene which was formed by the Wolff rearrangement of dibenzoyldiazomethane. On the other hand, when bis(1,1,1‐trifluoroacetylacetonato)copper(II) was used instead of rhodium(II) acetate dimer, the corresponding 1,4‐oxathiocin‐7‐carbonitriles 2 and/or 3 were obtained. The formation of 2 could be explained by the mechanism involving the sulfonium ylide derived from the dibenzoylcarbenoid and 1 .