Enantioselective addition aryl transfer reactions

In addition, in 2007, Jprgensen and co-workers [117] developed asymmetric a-arylation of aldehydes by reaction with quinones. The a-arylation proceeded in high yields, and the corresponding optically active a-arylated aldehydes were obtained with excellent enantioselectivities (up to 99% ee). Based on the proposed mechanism, this transformation proceeds via an addition/proton-transfer reaction sequence resulting in formal a-arylation. 

The group of Miyaura [78, 89] applied arylbismuth compounds [88] in these metal-catalyzed reactions. The application of this compound type in such met2il-catalyzed reactions is stiU rare. In fact, as has already been mentioned, Miyaura s group reported the use of chiral phosphane/dicationic palladium(II) complexes (based on (S,S)-Chiraphos and (S,S)-Dipamp) in the 1,4-addition of triaryl-bismuth reagents to cyclic and acyclic enones in aqueous methanol at low temperature (Scheme 5.32). Enantioselectivities of up to 95% ee were achieved for cyclic enones. The use of Cu(BF4)2 to help the reoxidation of Pd(0) to the catalyticaUy active Pd(II) species was an advantage, as well as the efficiency of the aryl transfer, allowing utilization of 2-2.8 of the three phenyl groups on the bismuth atom. Several years ago, Yamamoto, Nishikata, and Miyaura [68c] published a personal account of... 

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