Abstract
Rhodium-catalyzed asymmetric addition of cyclopropylboronic acids to electron-deficient alkenes such as alkenylsulfones, enones, enoates, and nitroalkenes proceeded to give high yields of the corresponding 1,4-addition products with high enantioselectivity.
Highlights
Rhodium-catalyzed asymmetric addition of cyclopropylboronic acids to electron-deficient alkenes such as alkenylsulfones, enones, enoates, and nitroalkenes proceeded to give high yields of the corresponding 1,4-addition products with high enantioselectivity
Asymmetric conjugate addition of organometallic reagents to electron-deficient alkenes catalyzed by Rh complexes is wellrecognized to be one of the most reliable methods for carbon– carbon bond formation introducing aryl and alkenyl groups with high enantioselectivity.[1,2]
As rare examples of the rhodium-catalyzed addition reaction of alkyl metal reagents, we reported asymmetric methylation of imines by the use of Me2Zn or trimethylboroxine as a methylating reagent, where the b-hydrogen to be eliminated does not exist.[5,6] von Zezschwitz and co-workers reported asymmetric 1,2- or 1,4-addition of Me3Al to cyclic enones catalyzed by a rhodium/ binap complex.[7]
Summary
Rhodium-catalyzed asymmetric addition of cyclopropylboronic acids to electron-deficient alkenes such as alkenylsulfones, enones, enoates, and nitroalkenes proceeded to give high yields of the corresponding 1,4-addition products with high enantioselectivity. An enantioselective addition was achieved by the use of chiral diene ligands.[14] A Rh complex coordinated with a ferrocenyl (Fc)-substituted diene ligand based on the tetrafluorobenzobarrelene (tfb) framework,[15] which is a superior catalyst in the asymmetric addition of arylboronic acids to alkenyl sulfonyl compounds,[16,17] displayed a high catalytic activity and enantioselectivity to give 3a in 96% yield with 97% ee (entry 2). Alkenyl sulfones substituted with 2-methyl-1propenyl (1e), butyl (1f), and benzyl (1g)[21] are good substrates
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