225. Nucleofilic 1,2-Shifts of Carboxamide Groups in the Benzil-Benzilic Acid Type Rearrangement of 4-Aryl-2,3-dioxobutyramides and of Quinisantine

Article abstract of DOI:10.1002/hlca.19850680807

4-Aryl-2,3-dioxobutyramide hydrates 1 undergo the benzyl-benzilic acid rearrangemet to form (substituted) benzyltartronate monoamides 2.For compound 1a (Ar = Ph), it is demonstrated by isotopic labeeling 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 procceding via an alkali-catalysed step, can reach a plateau in the k_obs/-> diagram (cf. the Fig.), due to complet formation of a mono-anion, and a further increase of the rate attributable to the rearrangement of a bis-anion.Comparison suggest that rearrangement involving an amide group are slower than those involving an ester group, and for this effect (as for others), the pre-equilibrium deprotonated of the hydrate is more important than a specific migration tendency.