Yamashita Y, Minami K, Saito Y, Kobayashi S. Development of a Simple Adjustable Zinc Acid/Base Hybrid Catalyst for C-C and C-O Bond-Forming and C-C Bond-Cleavage Reactions.
Chem Asian J 2016;
11:2372-6. [PMID:
27400735 DOI:
10.1002/asia.201600682]
[Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2016] [Indexed: 11/11/2022]
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).
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