A Convenient Procedure for he Synthesis o 2,3,4,6-Tetra-O-benzyl-D-gluconolactam and D-Nojirilactam

Swern oxidation of 2,3,4,5-tetra-O-benzyl-D -glucose ( 1 ) followed by ammonolysis gave the crystalline amide 3 which was oxidized (DMSO/pyridine · SO₃) to yield the oxo-amide 4 and the hydroxy-lactams 5 and 6 . Cyclization of 4 to the very slowly equilibrating 5 and 6 was completed by treatment with AcOH in CHCl₃. The configuration of the hydroxy-lactams was assigned on the basis of NOEs. Reduction (Et₃SiH/BF₃ · Et₂O) of the hydroxy-lactams either individually or as a mixture led to 2,3,4,6-tetra-O-benzyl-_D-gluconolactam ( 7 ). The procedure, based upon modifications of a patent, does not require chromatography; the overall yield of 7 from 1 is 43%. Hydrogenolysis of 7 gave _D-nojirilactam ( 8 ); benzylation led to the known pentabenzyl-_D-nojirilactam ( 9 ) and to the unsaturated lactam 10 .