Motoi Yogo

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

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.

Pyrimidine derivatives and related compounds. Part 42. Isolation of the intermediates in the ring transformation of 1,3-oxazine-2,4-diones into pyrimidines and pyrazoles, and their structure determination by 15N nuclear magnetic resonance analysis

Reaction of the 6-methyl-1,3-oxazine-2,4-diones (1) and (2) with hydrazine hydrate at room temperature gave the 6-hydroxy-5,6-dihydrouracils (7a) and (8a). The structures of the products were determined by 15N n.m.r. analysis. The mechanism of the ring transformation of 1,3-oxazines into pyrimidines and pyrazoles is discussed.

Novel reaction of uracil derivatives possessing electron-withdrawing groups at the 5-position with amines: exchange reaction between the N1-portion of uracils and amines

The reaction of 1,3-disubstituted uracils possessing an electron-withdrawing group such as nitro, carbamoyl, and cyano at the 5-position with primary amines resulted in the exchange of the N1-portion of the uracil ring with the amine moiety. The exchange reactions were influenced by the nature of substituents at the 5- and N1-position. The reaction sequence is explained in terms of addition, ring-opening, and ring-closure.

Novel ring tansformation of 1,3-oxazines into pyrroles by the reaction with soft cyanide anion

Treatment of 2H-1,3-oxazine-2,4(3H)-diones (1) with potassium cyanide caused a ring transformation to afford 5-imino-1,5-dihydro-2H-pyrrol-2-ones (2).