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

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Abstract4‐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 kobs./[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.