Synthesis of 5-iminopyrrol-2-one derivatives from 1,3-oxazines. Ring transformations via attack on the 2- or 6-position of 1,3-oxazines

Abstract

Reaction of the 2H-1,3-oxazine-2,4(3H)-dione derivatives (1) with potassium cyanide resulted in a ring contraction to give the corresponding 5-imino-1,5-dihydro-2H-pyrrol-2-ones (2), together with the 3-acetyl-4-amino-1H-pyrrole-2,5-diones (3) or the (E)-3-cyanoacrylamides (5). Irradiation of the (E)-3-cyanomethacrylamide (5b) in the presence of a catalytic amount of potassium cyanide also afforded the cyclized 5-iminopyrrol-2-one (2d). Further treatment of the iminopyrroles (2a–c) and (2e) with hydrochloric acid furnished the corresponding 1H-pyrrole-2,5-dione derivatives (4a–d). A mechanism involving initial attack on the 2- or 6-position of 1,3-oxazines is proposed for the ring transformations. This is the first example of ring transformation via attack on the 6-position.