Hydrosilylation conjugated enones

To date, the reductive cyclization of allenic alkenes remains undeveloped. However, the reductive cyclization of activated alkene partners in the form of 1,3-dienes and conjugated enones has been achieved using late transition metal catalysts. Indeed, the hydrosilylative dimerization of 1,3-dienes reported in 1969 appears to be the first reductive... 

Employment of chiral bis(oxazolinylphenyl)amines such as SJS)-BopsL-dpm (Scheme 4-328) as ligands for iron catalysts leads to almost quantitative yields and high enantioselectivities for the asymmetric hydrosilylation of ketones and asymmetric conjugate hydrosilylation of enones with (diethoxy)methylsilane as reductant (Scheme 4-329). Both enantiomers of the hydrosilylation product can be obtained from the same chiral ligand by a slight variation of the reaction conditions. The mixed catalyst system of (S -Bopa-dpm and iron(II) acetate provides the (/ )-enantiomer of the alcohol... 

In total, over the past six years, the chelating P,N-ligands have shown considerable promise in a variety of enantioselective processes, including transfer-hydrogenation and hydrosilylation of ketones, hydroboration of alkenes, conjugate addition to enones and Lewis-acid catalysed Diels-Alder reactions, in addition to those described above.128,341 It is anticipated that this list will continue to grow, and... 

In addition to molecules containing prochiral sites, racemic molecules can participate in catalytic asymmetric transformations. In some transformations, the stereocenter is destroyed in the course of the reaction, and equilibrating prochiral intermediates are formed. An example of such a process is the asymmetric arylation of ketones (Figure 14.8C). In other cases, one of the enantiomers of the substrate reacts with the asymmetric catalyst significantly faster than the other enantiomer. In this case, an enantioenriched product is formed, and the opposite enantiomer of the reactant remains. This last process is called a kinetic resolution and is illustrated for the conjugate reduction of enones via hydrosilylation (Figure 14.8D). In this case, the top and bottom faces of the C-C double bond are diastereotopic because reaction at each face of the enone generates diastereomeric products. This section of the chapter first presents the principles that relate to reactions at prochiral centers of achiral substrates and then presents the principles that relate to reactions of racemic or meso compounds. 

Racemic Rh-BINAP catalyst has been employed in the arylation of enones with ArInCl2, which proceeds in THF-MeOH at 110 Conjugate hydrosilylation of diarylacrylates Ar Ar C=CHC02R with (EtO)2MeSiH, catalysed by the Rh-Phebox complex (515), has been reported to proceed with <99%... 

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