Chiral Tetrafluorobenzobarrelenes as Effective Ligands for Rhodium-Catalyzed Asymmetric 1,4-Addition of Arylboroxines to β,β-Disubstituted α,β-Unsaturated Ketones

摘要

The catalytic asymmetric 1,4-addition of organometallic reagents to β,β-disubstituted α,β-unsaturated compounds offers a straightforward way of constructing all-carbon quaternary stereocenters. Although some copper-catalyzed processes have appeared in combination with highly reactive nucleophiles, such as diorganozinc, Grignard, and triorganoaluminum reagents, the use of air-stable, easily handled organoboronic acid derivatives would be desirable in view of the mildness of the reaction conditions. Unfortunately, however, applicable substrates have so far been limited to α,β-unsaturated pyridyl sulfones and 3-substi-tuted maleimides under rhodium catalysis. Herein, we describe that simple β,β-disubstituted α,β-unsaturated ketones can now be employed as substrates for the rhodium-catalyzed 1,4-addition of arylboroxines (arylboronic acid anhydrides) and that highly efficient asymmetric catalysis can be realized by using a chiral tetrafluorobenzobarre-lene as the ligand.