Iridium(III)-Catalyzed Enantioselective Si−H Bond Insertion and Formation of an Enantioenriched Silicon Center

摘要

Recently, synthetic application of the compounds possessing silylngroup(s) has been rapidly increasing,1 and the development of theirnefficient synthesis is a topic of interest. Although various methodsnare available for the preparation of silyl compounds, asymmetricnSi-H functionalization is a direct method for the preparation ofnchiral compounds possessing silyl group(s). In particular, asymmetricnSi-H insertion of a metal carbenoid derived from R-diazocarbonylncompounds is a potentially attractive route to producenchiral R-silylcarbonyl compounds.2 To date, copper(I) and rhodium(nII) complexes have been widely used as the catalyst for thisntype of reaction. In 1996, Doyle and Moody reported a seminalnstudy on enantioselective Si-H bond insertion with chiral dirhodium(nII) catalysts in the presence of R-phenyl-R-diazoacetate, albeitnwith moderate selectivity.3,4 Subsequent to this, Davies and coworkersnreported that Si-H insertion of R-alkenyl-R-diazoacetatencatalyzed by the rhodium(II) (S)-N-[p-(dodecylphenyl)sulfonyl-n]prolinate complex proceeded with good to high enantioselectivityn(77-95% ee).5 Panek and Jacobsen reported that a chiral copper-nSchiff base complex catalyzed Si-H insertion using R-phenyl-Rdiazoacetatenwith moderate to good yield and enantioselectivity (upnto 88% ee).6 Ge and Corey reported that a N-nonafluorobutanesulfonylprolinenrhodium(II) complex was a good catalyst for Si-Hninsertion using R-diazocyclohexenone derivatives.7 Moreover, Zhounand co-workers reported that a copper/chiral spiro-diimine catalystnshowed high enantioselectivity (93-99% ee) in the Si-H insertionnusing ArC(N2)CO2Me, while the reaction with MeC(N2)CO2Et hadnmodest enantioselectivity and a moderate yield.8 Still, the reactionnusing RC(N2)CO2Et (R ) acyclic alkyl group) that readilynundergoes u0001-hydride elimination2a,9 is a challenging researchntarget.8,10