Heterocycles from substituted amides. VIII Oxazole derivatives from reaction of isocyanates with 2‐isocyanoacetamides

A facile reaction of 2‐isocyanoacetamides 1 with reactive aryl and sulfonyl isocyanates is shown to give 5‐amino‐2‐oxazolecarboxamides 3 in a reaction arising from electrophilic attack of isocyanate with the nucleophilic isocyanide carbon. This reaction, perhaps proceeding through an unstable nitrile ylid intermediate reminiscent of the Cornforth rearrangement, is a first example of ring closure via acylation, involving the activated methylene of an organic isocyanide, without recourse to added base. Isomeric 5‐amino‐4‐oxazolecarboxamides 4 are formed when 5‐aminooxazoles 2 react with isocyanates. Since 2 has previously been shown to easily form by thermal isomerization of 1 , methods now exist for the preparation of both 5‐amino‐ 2‐ and 4‐oxazolecarboxamides from the single starting material 1 . In contrast, 1 with acyl isocyanates is shown to give a variety of products, including iminooxazolinediones, 5‐amino‐2‐oxazolecarbox‐amide 3 and 2 (1) pyrazinones (tentatively identified), depending on the structure of the isocyanates.