Syntheses of Cyclic Hydroxamic Acids and Lactams with 2,3-Dioxo-1,4-benzoxazine Skeleton

Article abstract of DOI:10.1002/prac.19933350409

Ethyl 2-nitrophenyl oxalate (1a) and its 5-methoxy derivative (1b) were subjected to catalytic hydrogenations over 3percent Pt (S) on carbon in different solvents.Thus, hydrogenation in acetic acid yielded 4-hydroxy-2,3-dioxo-1,4-benzoxazine (2a) and its 7-methoxy derivative (2b) by reductive cyclization, the dehydro forms of the naturally occurring cyclic hydroxamic acids DIBOA and DIMBOA from Gramineae.In contrast, hydrogenation of esters 1 in methanol results in the formation of amides 3 by acyl group migration.On heating, amides 3 undergo lactonization to form lactone-lactames 4, which in turn undergo ring opening to give amides 3 when refluxed in ethanol.