We reported that the rhodium-catalyzed carbonyl-directed catalytic asymmetric hydroborations (CAHB) of certain (E)- and (Z)-disubstituted and trisubstituted-�,?-unsaturated amides and esters proceed with high regio- and ?-facial selectivity to give chiral organoboronates. We now report that the efficient directed-CAHB of ?,d�unsaturated cyclopentenyl carboxamides affords chiral organoboronates via enantioselective desymmetrization. In contrast to the �,?-unsaturated acyclic substrates in our previous studies, the carbonyl-directed enantioselective desymmetrization of these meso-substrates requires re/si-site selectivity rather than p-facial discrimination. For example, ?,d�unsaturated amide 1  undergoes CAHB with 4,4,6�trimethyl�1,3,2�dioxaborinane (tmdBH  ) using Rh(nbd)2BF4 in conjunction with (BINOL)PN(Me)Ph (L1  ) to give the cis�?�hydroxyamide 3  in 80% yield and 94% ee after oxidation. The isolated chiral secondary organoboronate 2 also undergoes palladium-catalyzed cross coupling with a variety of simple aryl halides. The presentation will discuss our current results and a proposed catalytic cycle based on DFT calculations carried out for a model reaction.

Enantioselective desymmetrization via carbonyl-directed catalytic asymmetric hydroboration

247th National Meeting (2014)

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