Tetronic acids and derivatives. Part XI . Structure of coupling products of tetronic acids with benzenediazonium sulfate

Abstract

13C Nmr, 'H nmr and ir parameters of coupling products of tetronic acids (4-hydroxy-SH-furan-2-ones) with benzene diazonium sulfate are only consistent with a phenylhydrazone formulation with an almost equal ratio of the syn and anti configurations. These results contrast with those of coupling products of acyclic 3-ketoesters, existing mainly as anti tautomers, and more sharply with the 3-parabromophenylhydrazone of L-dehydro ascorbic acid, which is exclusively syn.