Beckmann rearrangement migratory aptitude

Dimethyl [a-(hydroxyimino)benzyl]phosphonate is stable in mineral acid but decomposes in formic acid containing formate with the liberation of benzonitrile, but otherwise the behaviour is different from that in boiling acetic acid when an additional product, a phosphoramidate ester, is obtained by a Beckmann rearrangement. For the oximes of the (4-methoxybenzoyl)- or (4-chlorobenzoyl)-phosphonic esters, only the phosphoramidate diester 127 is obtained, but for all the substrates examined [additionally the unsubstituted benzoyl- as well as the (4-methylbenzoyl)phosphonic derivatives], the formation of the phosphoramidate ester demonstrates a high migratory aptitude of the phosphinoyl group (Scheme 22) ... 

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