Abstract

Mixed anhydrides derived from carboxylic and amidophosphoric acids, (RO)(R′2N)P(O)OC(O)R″ (1), undergo unimolecular fragmentation yielding carboxyamides, R″C(O)NR′2, and metaphosphate esters, ROPO2. The mechanism of the amino group transfer was studied for substrate 1a (1, R = R′ = Me; R″ = Ph); solvent as well as substituent effects indicate little (if any) charge development in the transition state. The effects of solvents and Lewis acids on the reaction rate and the activation parameters determined for 1a can be explained best in terms of stabilizing interactions with either carboxyamide or metaphosphate being formed in the course of reaction. The transfer of a functional group from one acyl center to another was investigated for other anhydride systems and the relative contributions of the fragmentation vs. disproportionation of substrates are discussed.

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