Spontaneous Lossen Rearrangement of (Phosphonoformyl)hydroxamates. The Migratory Aptitude of the Phosphonyl Group

CLAUDIO SALOMON; BREUER E.

JOURNAL OF ORGANIC CHEMISTRY

AMER CHEMICAL SOC

Lugar: Washington; Año: 1997 vol. 62 p. 3858 - 3861

0022-3263

(i-PrO)2P(dO)COSEt (1) reacted with NH2OH in pyridine at room temperature to give mainly (iPrO)2P(dO)NH2 (4). The formation of 4 was interpreted in terms of a spontaneous Lossen rearrangement of (i-PrO)2P(dO)CONHOH (2a) formed in the reaction. A transient 31P NMR signal appearing in the reaction mixture at δ -1.8 was assigned to 2a. Trapping of (i-PrO)2P(dO)NdCdO (5), formed in the reaction of 1 and NH2OH, by cyclohexylamine gave (i-PrO)2P(dO)NHCONHC6H11 (6). Attempted isolation of 6 gave the hydrolyzed product N-cyclohexylurea (7). The reaction of 1 with NH2OMe proceeded slower than that with NH2OH and gave the expected (i-PrO)2P(dO)- CONHOMe (2b), which was isolated and identified. 2b converts slowly to 4 in pyridine at room temperature. In contrast, MeNHOH reacted rapidly with 1 and gave the stable crystalline (iPrO)2P(dO)CON(Me)OH (2c). The structure of hydroxamates 2 were assigned on the basis of 1H, 13C, and 31P NMR spectral data. This facile Lossen rearrangement is discussed in terms of the unusually high migratory aptitude of the phosphonyl group.