Blepharin, the β-D-glucoside (1) of 2-hydroxy (2H, 4H)-1, 4-benzoxazin-3-one(III), isolated from Blepharis edulis Pers., has been diaselectively synthesised from 2-hydroxy-(2H, 4H)-1, 4-benzoxazin-3-o-ne. The latter was obtained from isatin via a novel ring expansion reaction followed by glucosidation with 2,3,4,6-tetra-O-acetyl-β-D-glucopyranose and mild hydrolysis.