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Enantioselective rhodium-catalyzed hydroboration is becoming an increasingly important asymmetric transformation of alkenes based upon the utility of the organo boranate ester intermediate. The newly acquired asymmetric C-B bond can be converted to C-O, C-N, C-C bonds and the organo borante can be coupled to SP2 hybridized halogen bonds, all with retention of configuration. Catalyzed hydroboration of 1,1-disubstituted alkenes are an especially challenging substrate class for this enantioselective transformation. The difficulty for catalysts to distinguish between the two enantiotopic faces of the olefin is one of the major issues that have to be overcome to achieve a desirable level of enantioselectivity. Rhodium catalyzed hydroboration of the 1,1-disubstituted alkenes gives the expected anti-Markovnikov’s regio-chemistry products in high yields. Herein is reported our groups progress in the rhodium catalyzed hydroboration of the 1,1-disubstituted allyl sulfonamide substrate class utilizing monodenate ligands with our best results to date being with sulfonamide 25 and Rh(nbd)2BF4, L6f and pinacol borane (99% yield, 67.7% ee).
Adviser: James M. Takacs