Preparation of α-(2,2-diphenylhydrazino)- and α-(benzyloxyamino)-lactones by radical cyclization: use of glyoxylic acid diphenylhydrazone and glyoxylic acid O-benzyloxime

Glyoxylic acid diphenylhydrazone (2, Y = NPh 2 ) and the corresponding O-benzyloxime (2, Y = OBn) are easily esterified in high yield by β-bromo alcohols, and the resulting esters undergo radical cyclization to α-(2,2-diphenylhydrazino) or α-(benzyloxyamino) lactones on treatment with tributyltin hydride; the initial radical can be formed by homolysis of a carbon–selenium bond as well as a carbon–bromine bond and, when applied to appropriate alcohols, the esterification–radical closure sequence can also be used to make six- or seven-membered lactones.