A cationic oxazaborolidinium-catalyzed asymmetric Mukaiyama aldol reaction of (1-methoxy-2-methyl-propenyloxy)-trimethylsilane with various aldehydes including α,β-disubstituted acroleins has been developed in high yields and enantioselectivities. The synthetic utility of this methodology was demonstrated in the first short synthesis of naturally occurring inthomycin C in high enantiopurity.

A catalytic synthetic route to highly functionalized chiral cyclopropane derivatives was developed by Michael-initiated cyclopropanation of α-substituted acroleins with aryl- and alkyl diazoacetates. In the presence of chiral (S)-oxazaborolidinium cation 1b as a catalyst, the reaction proceeded in high yield (up to 93%) with high to excellent diastereoselectivity (up to 98% de) and enantioselectivity (up to 95% ee).

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This paper describes a catalytic enantioselective route to synthesize functionalized all-carbon quaternary acyclic systems via a boron Lewis acid-promoted formal C-C insertion of diazoesters into aryl-CHO bonds. In the presence of chiral (S)-oxazaborolidinium cation 1d as a catalyst, the reaction proceeded in good yield (up to 83%) with good regioselectivity (up to 88:12) and excellent enantioselectivity (up to 99% ee). The synthetic potential of this method was illustrated by conversion of the products to both α- and β-amino esters.

A catalytic route to highly functionalized chiral 2-pyrazolines by an asymmetric 1,3-dipolar cycloaddition reaction of ethyl diazoacetate with alpha-substituted and alpha,beta-disubstituted acroleins has been developed; in the presence of chiral (S)-oxazaborolidinium ion as catalyst, the reaction proceeded with high to excellent enantioselectivities (up to 99% ee).

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A catalytic enantioselective formal [2+2] cycloaddition between a-halo acroleins and electronically diverse arylalkenes is described. In the presence of (S)-oxazaborolidinium cation as the catalyst, densely functionalized cyclobutanes containing two vicinal tetrasubstituted stereocenters were produced in high yields and high diastereoselectivities with excellent enantioselectivities. Mechanistic studies revealed that the cis isomer could be transformed into the trans isomer via an enantiocontrolled process. A gram-scale reaction of this catalytic method was used to demonstrate its synthetic potential. Scheme 1. Chiral Lewis acid catalyzed asymmetric [2+2] cycloadditions.

A metal-free route to 1,4-disubstituted and 1,4,5-trisubstituted formyl triazoles was developed. One 1,2,3-triazole containing diastereotopic protons was identified.