The enantioselective protonation is an fascinating method for preparing tertiary chiral carbon centers, usually found in valuable building blocks of biologically active natural products. Recently, our group developed a new type of chiral proton donor by combination of chiral Lewis acid-oxazaborolidinium ion with carboxylic acid. We applied this new chiral Lewis acid assisted Brønsted Acid (chiral LBA) to synthesize chiral β-acyloxy substituted esters. This chiral LBA was highly effective proton donor for asymmetric O-H insertion reaction. The reaction proceeded in good yields (up to 97%) with excellent stereoselectivities (up to 99% ee).<br/>The synthetic utility of this methodology was demonstrated in the short synthesis of (S)-tropic acid methyl ester which is a derivative of (S)-tropic acid. (S)-Tropic acid is an important building block for biologically active tropane alkaloids. These series of reaction was also available in gram-scale with good result. For a better understanding of reaction mechanisms, our group performed deuterium experiment and KIE(kinetic isotope effect) and proposed transition-state model.

Stereoselective O-H insertion of <i>α</i>-benzyl diazoesters by carboxylic acids activated by chiral oxazaborolidinium ion

254th National Meeting (2017)

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Stereoselective O-H insertion of α-benzyl diazoesters by carboxylic acids activated by chiral oxazaborolidinium ion