Phosphorus organic synthesis. X. tert-butyl carbamate. An efficient additive in modified curtis reaction by diphenyl phosphorazidate (DPPA).

Abstract

A modified Curtius reaction of N-benzyloxycarbonyl-L-proline (I) with diphenyl phosphorazidate (DPPA) in the presence of triethylamine in tert-butyl alcohol afforded the allophanate (III) as the major product but the expected carbamate (II) as a minor product. Similar result was obtained in the case of the ordinary Curtius reaction of I. However, the use of tert-butyl carbamate (X) as an additive changed the reaction course and the desired carbamate (II), though accompanied by racemization, was obtained in good yield.