Development of a Simple Adjustable Zinc Acid/Base Hybrid Catalyst for C−C and C−O Bond‐Forming and C−C Bond‐Cleavage Reactions

Abstract

A newly designed zinc Lewis acid/base hybrid catalyst was developed. By adjusting the Lewis acidity of the zinc center, aldol-type additions of 2-picolylamine Schiff base to aldehydes proceeded smoothly to afford syn-aldol adduct equivalents, trans-N,O-acetal adducts, in high yields with high selectivities. NMR experiments, including microchanneled cell for synthesis monitoring (MICCS) NMR analysis, revealed that anti-aldol adducts were formed at the initial stage of the reactions under kinetic control, but the final products were the trans-(syn)-N,O-acetal adducts that were produced through a retro-aldol process under thermodynamic control. In the whole reaction process, the zinc catalyst played three important roles: i) promotion of the aldol process (C-C bond formation), ii) cyclization process to the N,O-acetal product (C-O bond formation), and iii) retro-aldol process from the anti-aldol adduct to the syn-aldol adduct (C-C bond cleavage and C-C bond formation).

Mechanochemical synthesis of Zn-bionanohybrids: size effect at the nanoscale to improve their enzyme-like activity

“…[11][12] In particular, the synthesis of Zn catalysts has attracted great interest due to its high abundance in the earth's crust (0.0076%), its affordability, and its non-toxicity. 13 Surprisingly, the interest in zinc as a catalyst has been underdeveloped, but recently this situation is changing 14 and the potential of zinc has been demonstrated in several applications such as C-C, C-N and C-O bond formation reactions, [15][16][17] and in solid surface reactions such as acylation of alcohols, phenols and amines. [18][19] Therefore, the development of methods for the synthesis of highly active, selective, stable and robust zinc nanoparticles (ZnNPs) is of great interest.…”