Phosphazenes reactions with carboxylic acid derivative

Reaction of Phosphazenes with Carboxylic Acid Derivatives... 

The phosphazene bases BTPP and Bu-P2 mediate the rearrangement of unactivated A -alkyl-(9-benzoyl hydroxamic acid derivatives to give 2-benzoyl amides. The rate of reaction was found to be dependent upon the steric nature of the A -alkyl substituent [39a]. Treatment of malonyl derived (9-acyUiydroxamic acid derivatives with the phosphazene superbase Bu-P2 gives 2,3-dihydro-4-isoxazole carboxylic ester derivatives. The rate and yield of the reaction depend upon the (9-acyl substituent [36b] (Scheme 5.21). 

Clark, A.J., Al-Faiyz, Y.S.S., Patel, D. and Broadhurst, M.J. (2001) Rearrangement of unactivated A-alkyl-O-benzoyl hydroxamic acid derivatives with phosphazene bases. Tetrahedron Letters, 42, 2007-2009 Clark, A.J., Patel, D. and Broadhurst, M.J. (2003) Base-mediated reaction of A-alkyl-O-acyl hydroxamic acids synthesis of 3-oxo-2,3-dihydro-4-isoxazole carboxylic ester derivatives. Tetrahedron Letters, 44, 7763-7765. 

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