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Preparation of α-(2,2-diphenylhydrazino)lactones and related compounds by radical cyclization: Use of glyoxylic acid hydrazone derivatives
Clive,Zhang,Subedi,Bouetard,Hiebert,Ewanuk
, p. 1233 - 1241 (2007/10/03)
Glyoxylic acid diphenylhydrazone (2a) and the corresponding O-benzyloxime (2b) are easily esterified in high yield by β-bromo alcohols. The resulting esters undergo radical cyclization to α-(2,2-diphenylhydrazino)- or α-[(phenylmethoxy)amino]lactones on treatment with tributyltin hydride. Esters for radical cyclization were also made using a β-(phenylseleno) alcohol and an enol ether. Several derivatives of glyoxylic acid were evaluated, but none was as effective as 2a or 2b. The imine 28 was prepared by an indirect route; it undergoes radical cyclization with displacement of the nitrogen substituent (28 → 30) so that an α-amino lactone can be generated by acid hydrolysis of the cyclization product.