AN EFFICIENT AND SIMPLE ENTRY TO N-SUBSTITUTED BETA-ENAMINO ACID-DERIVATIVES FROM 2-ALKYL-2-OXAZOLINES AND 2-ALKYL-2-THIAZOLINES

Reaction of azaenolates of 2-alkyl-oxa(thia)zolines 6 with imidoyl chl orides 7 as electrophiles to furnish masked N-substituted beta-enamino acid derivatives 1-2 in 70-90% yield is described. Alternative routes are discussed. Compounds 1-2 generally appear in one tautomeric form, imino or enamino, depending on the nature of the imidoyl chloride. Th e configuration of the enamino moiety (Z) and the conformation (s-cis) of compounds 1-2 obtained were established by an NMR study and unequi vocally set by nuclear Overhauser effect difference experiments. An X- ray structure of compound le is also reported, showing a strong intram olecular NH ... N hydrogen bond. Ab initio calculations (HF/3-21G and HF/3-21+G) have been carried out on several representative examples (l e, Ip, and II) in an attempt to support and provide the correct geomet ry of these derivatives. Structural considerations among the possible isomers of compounds 1 are discussed. From these studies it was conclu ded that the theoretical calculations agree with the experimental resu lts. In addition, a very simple one-pot procedure for the preparation of masked N-substituted alpha>-alkylated beta-enamino acid derivatives 2 from 6, 7, and different alkyl halides (R(3)Y) is described.