CYCLIZATION OF 1,5-DINITRILE SYSTEMS WITH HYDROGEN HALIDES - A SEARCHFOR THE UNDETECTED KEY TAUTOMER

The C-13 NMR spectra of the pyridones 7a-d recorded in DMSO-d(6) show three groups of signals which correspond to the two diastereomers of t he 7-exo tautomer and the 7-endo tautomer. The X-ray powder analysis a nd the molecular structures of 7a-c clearly prove that these compounds . and probably 7d, are present in the solid state as a single diastere omer of the 7-exo tautomer which, on being dissolved, establishes an e quilibrium with the other diastereomer through the 7-endo tautomer Thi s later had been proposed as a key intermediate in the cyclization of the 1,5-dinitrile system present in 7a-d but was not previously detect ed. (C) 1997 Elsevier Science Ltd.