Room-Temperature Rhodium-Catalyzed Asymmetric 1,4-Addition of Potassium Trifluoro(organo)borates

For the first time the room-temperature rhodium-catalyzed asymmetric 1,4-addition of potassium aryltrifluoroborates to α,β-unsaturated substrates is described. Thanks to the use of a chiral diene as ligand for rhodium and triethylamine as base, to facilitate transmetalation of the boron species, high yields and enantioselectivities were generally achieved. Moreover, the use of such tetravalent boron species offers some improvements compared to the use of boronic acids in term of stability and ease of purification.