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

( i -PrO) 2 P( O)COSEt ( 1 ) reacted with NH 2 OH in pyridine at room temperature to give mainly ( i- PrO) 2 P( O)NH 2 ( 4 ). The formation of 4 was interpreted in terms of a spontaneous Lossen rearrangement of ( i- PrO) 2 P( O)CONHOH ( 2a ) formed in the reaction. A transient 31 P NMR signal appearing in the reaction mixture at δ −1.8 was assigned to 2a . Trapping of ( i- PrO) 2 P( O)N C O ( 5), formed in the reaction of 1 and NH 2 OH, by cyclohexylamine gave ( i- PrO) 2 P( O)NHCONHC 6 H 11 ( 6 ). Attempted isolation of 6 gave the hydrolyzed product N -cyclohexylurea ( 7 ). The reaction of 1 with NH 2 OMe proceeded slower than that with NH 2 OH and gave the expected ( i- PrO) 2 P( O)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 ( i- PrO) 2 P( O)CON(Me)OH ( 2c ). The structure of hydroxamates 2 were assigned on the basis of 1 H, 13 C, and 31 P NMR spectral data. This facile Lossen rearrangement is discussed in terms of the unusually high migratory aptitude of the phosphonyl group.