DOUBLE CYCLISATION OF PHENYLGLYCINE-o-CARBOXYLIC ACIDS - I NEW STABLE MESOIONIC OXAZOLONES

Article abstract of DOI:10.1016/0040-4020(80)85053-8

Remarkably stable mesoionic oxazolones possessing an oxazolo<3,2-a>quinolinium structure (5a-b, 8, 16, 17) were obtained by the double cyclisation of phenylglycine-o-carboxylic acids (3a-c) in refluxing acetic anhydride or in benzoic anhydride at 140 deg.The O-Ac group was eliminated to give the corresponding lactones (6a-b) or replaced by O-Ts (7).IR stretching vibrations of the endo-carbonyl were in the range 1710-1768 cm^-1, while ν_1-CH exhibited unusually high values (3159-3194 cm^-1). 1-Acyl derivatives could be obtained only with TFAA (23-24), although easydeuteration of the same position took place in the presence of traces of trifluoroacetic acid.Hydrolysis of 5b led to the α-quinolone-N-acetic acid 27a.In the case of 5a, hydrolysis was accompanied by self-acylation of the nucleophilic site at C-4 with formation of a dimeric acid 28a.The presence of an additional Me group in phenylalanine-o-carboxylic acid (36) activates the corresponding mesoionic oxazolone 37 so that 1-acylation becomes possible with formation of the fused oxazole 38 by the Dakin-West reaction.Temperature dependent magnetic non-equivalence of methylene protons has been observed in acids 3b-d and f and also in the 7-membered anhydride 48b.