No abstract

A new catalytic transesterification promoted by a tetranuclear zinc cluster was developed. The mild reaction conditions enabled the reactions of various functionalized substrates to proceed in good to high yield. A large-scale reaction under solvent-free conditions proceeded with a low E-factor value (0.66), indicating the high environmental and economical advantage of the present catalysis.

A catalytic amount of 4-dimethylaminopyridine showed drastic additive effects on transesterification catalyzed by the μ 4 -oxo-tetranuclear zinc cluster Zn 4 (OCOCF 3 ) 6 O, enhancing the catalytic activity by more than 15-fold. The new catalyst system facilitates transesterification of less reactive sterically demanding esters and alcohols.

Selective intermolecular oxidative cross-coupling of enolates, which is a bond-forming reaction between carbanion equivalents, remains as an unsolved issue despite its potential utility for the direct synthesis of unsymmetrical 1,4-diones. The main difficulty derives from the unavoidable homo-coupling. Our strategy depends on the selective one-electron oxidation of one enolate to afford an electrophilic carbonyl α-radical species, followed by trapping with another enolate. The present study demonstrates the selective oxovanadium(V)-induced cross-coupling between boron and silyl enolates.

Density functional theory calculations demonstrate that Al(III)-catalyzed conversion of glyoxal to glycolic acid proceeds via a 7-membered dual Lewis acid-hydrogen bonding activation transition state of the 1,2-hydride shift, rather than the previously proposed 5-membered metal-alkoxide chelate activation transition state.