A mechanistic investigation of the asymmetric Meerwein-Schmidt-Ponndorf-Verley reduction catalyzed by BINOL/AlMe3-structure, kinetics, and enantioselectivity

作者：Graves Christopher R; Zhou Hongying; Stern Charlotte L; Nguyen SonBinh T^*

来源：Journal of Organic Chemistry, 2007, 72(24): 9121-9133.

DOI：10.1021/jo070563u

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The kinetics of the Al-catalyzed asymmetric Meerwein-Schmidt-Ponndorf-Verley (MSPV) reduction are presented. Structural identification of the catalytic precursor formed in situ between (S)-2,2';-dihydroxy-1,1';-binapthyl ((S)-BINOL), AlMe3, and 2-propanol was established through H-1 and Al-27 NMR spectroscopies, and APCIMS. All experimental evidence points toward the formation of a BINOL-chelated, pentacoordinate aluminum species in solution. Ligand-accelerated catalysis was confirmed for the phenol ate/AlMe3/2-propanol system. The rate law for the catalytic reaction was determined to be nearly unimolecular dependent on aluminum, zero-order dependent on substrate, and inversely dependent on 2-propanol. At the low catalyst loading employed in the BINOL/AlMe3 system, the inherent reversibility of the MSPV reaction does not affect product yield or enantiomeric excess over time. Systematic ligand studies imply that while a tetrahedral geometry around the aluminum center may result in the most active MSPV reduction catalysts, the enantioselectivity of the reaction is enhanced when the aluminum center allows for a 2-point coordination of the substrate to achieve a pentacoordinate geometry with the fifth ligand weakly coordinated to the axial site of a pseudo square pyramid.

• 出版日期2007-11-23
• 单位西北大学