Abstract
Ethyl acetoacetate (I) and ethyl benzoylacetate (II) were each isonitrosated, reductively acylated with zinc and phenylacetyl chloride or benzoyl chloride, and submitted to dehydrative cyclization with phosphoryl chloride to form ethyl 2-R′-5-R-4-oxazole carboxylate (V:R=CH3, R′=C6H5CH2; VI:R=CH3, R′=C6H5; VII:R=C6H5, R′=C6H5CH2; VIII:R=R′=C6H5), and the same compound (IX) with R=C6H5 and R′=CH3 was prepared by the route described in Part I of this series. These esters were derived to the corresponding acids and hydrazides. N, O-Dibenzoyl-3-phenylserine ethyl ester (XII) was obtained by heating erythro-3-phenylserine ethyl ester hydrochloride (XI) and its threo isomer (XI) with benzoyl chloride in benzene. In the case of the threo compound (XI), an oxazolone (XIII) formed as a by-product. Catalytic reduction of ethyl α-benzoylhippurate (IV) gave erythro-N-benzoyl-3-phenylserine ethyl ester (XIV) whose treatment with phosphoryl chloride gave ethyl threo-2, 5-diphenyl-2-oxazoline-4-carboxylate (XV) when the reaction was carried out at room temperature and (XIII) when the reaction mixture was heated on a water bath. Application of phosphoryl chloride to (XII) at 50° afforded (XIII).
