Preparation of Heterocyclic Compounds from α-Oxoketene O, N-Acetals

Abstract

α-Oxoketene O, N-acetals 1 act as nucleophiles and electrophiles, and are demonstrated as good starting materials for the preparation of various heterocyclic compounds. They are prepared from β-oxothiono esters 2, which are easily prepared from carbon disulfide, in only mixing with primary amine in the presence of triethylamine. Acetals 1 are converted to pyrrolidine-2, 5-diones 3, 1, 6-naphthyridine-2, 5 (1H, 6H) -diones 4, 1, 2, 3, 4-tetrahydro-2-pyridinones 5, piperidine-2, 6-diones 6, pyrroles 7, 2H-1, 3-oxazine-2, 4 (3H) -diones 8, and 4H-pyran-4-one 12 by the reaction with electrophiles. On the other hand, acetals 1 also react with nucleophiles to yield pyrazoles 19, isoxazoles 22, and pyrimidines 24. β-Oxothiono esters 2 are also good substrates for the preparation of 3-ethoxypyrazoles 25, 3-ethoxyisoxazoles 28, and 4-ethoxypyrimidines 29.