Nucleophilic 1,2-Shifts of Carboxamide Groups in the Benzil-Benzilic Acid Type Rearrangement of 4-Aryl-2,3-dioxobutyramides and of Quinisatine

4-Aryl-2,3-dioxobutyramide hydrates 1 , undergo the benzil-benzilic acid rearrangement to form (substituted) benzyltartronate monoamides 2 . For compound 1a (Ar = Ph), it is demonstrated by isotopic labelling that the reaction occurs exclusively by migration of the CONH₂ group. Kinetic measurements with 1a-c and with the cyclic amide quinisatine 6 show that the rearrangement of the carboxamide group, proceeding via an alkali-catalysed step, can reach a plateau in the k_obs./OH^?] diagram (cf. the Fig.), due to complete formation of a mono-anion, and a further increase of rate attributable to the rearrangement of a bis-anion. Comparisons suggest that rearrangements involving an amide group are slower than those involving an ester group, and that, for this effect (as for others), the pre-equilibrium deprotonation of the hydrate is more important than a specific migration tendency.