The directed catalytic asymmetric hydroboration (directed-CAHB) of alkenes has been used to prepare a variety of chiral organoboronates. The latter are increasingly valuable as partners for cross-couplings with alkyl or aryl halides; in addition, methodologies are available for the stereospecific functional group interconversion of the C-B bond to C-O, C-N, or C-halide functionalities. Here, we present our recent developments on the rhodium-catalyzed directed-CAHBs of unsaturated oxime ethers. The studies reveal a number of surprising trends regarding the nature of the oxime derivative used, the nature of the borane employed, the nature of the chiral ligand employed, and the effect of substituents on the alkene undergoing CAHB. Using simple, chiral TADDOL-based phosphite and phosphoramidite ligands chiral organoboronate products are obtained in moderate-to-good yields (50-85%) and, in the case of the chiral tertiary organoboronate shown below, enantiomer ratios up to 92:8; see below. These and other recent results will be discussed.

Oxime ether-directed catalytic asymmetric hydroboration

248th National Meeting (2014)

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