Rh(I)-Catalyzed Asymmetric Hydrosilylation and Hydroboration/Oxidation Reactions Using Berens Ligand

Abstract

The Berens ligand 2 was used in a number of Rh(I)-catalyzed asymmetric hydrosilylations of acetophenones under standard conditions, affording the corresponding 1-arylalcohols in ees up to 65%. Some novel Rh catalysts were generated in situ from the neutral precatalyst [Rh(µ-Cl)(COD)]₂ and screened in the catalytic asymmetric hydroboration/oxidation of styrenes, gave enantioselectivities of up to 62%.

Keywords:

• Catalytic asymmetric synthesis
• chiral diphosphine
• hydroboration
• hydrosilylation

ACKNOWLEDGMENTS

We thank the Fundação para a Ciência e a Tecnologia and Programa Operacional Ciência e Inovação (POCI) for generous financial support of this work (POCI/QUI/55779/2004), including a grant (C.S.M.), which was partly funded by the European Community Fund Fundo Europeu de Desenvolvimento Regional (FEDER).

Notes

^a Determined by GC.

^b Determined by GC using a Cyclodex B capillary column.

^a Standard conditions: vinyl arene/CatBH/ligand/pre-catalyst 1/1.1/0.027/0.013 in THF, rt, ca. 15 h.

^b Determined by GC analysis.

^c The percentage ee of the branched alcohol was determined by chiral GC analysis (on a cyclosil-B capillary column).

^d The major isomer is indicated in parentheses.