SYNTHESES OF CYCLIC HYDROXAMIC ACIDS AND LACTAMS WITH 2,3-DIOXO-1,4-BENZOXAZINE SKELETON

Ethyl 2-nitrophenyl oxalate (1 a) and its 5-methoxy derivative (1 b) w ere subjected to catalytic hydrogenations over 3 % Pt (S) on carbon in different solvents. Thus, hydrogenation in acetic acid yielded 4-hydr oxy-2,3-dioxo-1,4-benzoxazine (2a) and its 7-methoxy derivative (2 b) 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 ami des 3 by acyl group migration. On heating, amides 3 undergo lactonizat ion to form lactone-lactames 4, which in turn undergo ring opening to give amides 3 when refluxed in ethanol.