Rh-Catalyzed Enantioselective Hydroalkenylative Cyclization of 1,6-Enynes Constructing All-Carbon Quaternary Stereocenters

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We report the enantioselective construction of all-carbon quaternary stereocenters (up to 99% ee) by the cationic Rh(I)/Segphos-catalyzed hydroalkenylative cyclization of 1,6-enynes with α-substituted acrylamides. This Rh catalysis proceeds with small excesses of alkenes at room temperature in most substrates to yield the desired cyclization products in high yields and enantioselectivity. Mechanistic studies indicate acrylamide-substituted C–H bond activation processes: for α-substituted acrylamides, the C–H bond is cleaved by a cationic Rh(III) complex (rhodacyclopentene); in contrast, for β-substituted acrylamides, the C–H bond is cleaved by a cationic Rh(I) complex.