Francis M. F. Chen, N. Benoiton
Mar 1, 1987
Citations
0
Influential Citations
42
Citations
Journal
Canadian Journal of Chemistry
Abstract
Pure mixed anhydrides R1OCO-Xxx-O-COOR2 (Xxx=NHCHRCO) have been obtained by reaction of N-alkoxycarbonyl-amino acids R1OCO-Xxx-OH with alkyl chloroformate R2OCOCl (R2 = methyl, ethyl, isobutyl, menthyl) in the presence of N-methylmorpholine or N-methylpiperidine (NMP) in dichloromethane at −5 °C, followed by washing the mixtures with aqueous solutions and removal of the solvent. R1OCO-Xxx-O-COOR2 (R2 = ethyl, tert-butyl) have been obtained by reaction of R1OCO-Xxx-O−•+HNMP with the corresponding dialkyl dicarbonates followed by the same work-up. Mixed anhydride generation is much slower when triethylamine is used as base. The initial reaction in the decomposition of mixed anhydrides is cyclization to the 2-alkoxy-5(4H)-oxazolone (R1O-oxazolone) followed by release of alcohol R2OH. Symmetrical anhydride (R1OCO-Xxx)2O and ester R1OCO-Xxx-OR2 are also formed. The ease of cyclization depends on R2, and is in the order methylsulfonylethyl (Ms) methyl/ethyl/isobutyl menthyl. R1OCO-Xxx-O-COOMs preparations conta...