Tetsuo Kogure

Reduction of carbonyl compounds via hydrosilylation : II. Asymmetric reduction of ketones via hydrosilylation catalyzed by a rhodium(I) complex with chiral phosphine ligands

Abstract Effective asymmetric reduction of alkyl phenyl, dialkyl and alkyl cyclohexyl ketones has been achieved via hydrosilylation, catalyzed by a rhodium(I) complex with optically active phosphine ligands using various hydrosilanes. A mechanism of the induction of asymmetry is proposed in view of the stereochemical course of the reaction.

The asymmetric hydrogenation of α-keto esters catalyzed by rhodium(I) complexes with chiral diphosphine ligands. On the catalytic cycles and the mechanism of asymmetric induction

Abstract Asymmetric hydrogenations of n-propyl pyruvate and ketopantoyl lactone catalyzed by rhodium complexes with (—) DIOP and BPPM were carried out under a variety of conditions. It was found that i) the Schrock-Osborn mechanism was not operative in these reactions at all since no acceleration of the reaction rate by the addition of water (1%) was observed, ii) there was a clear difference between cationic and neutral (in situ) rhodium catalysts in their enantioselectivity, and iii) there was a remarkable solvent effect on the extent and direction of asymmetric induction. Possible mechanisms are discussed on the basis of these results.

Reduction of carbonyl compounds via hydrosilylation: V. Synthesis of optically active allylic alcohols via regioselective asymmetric hydrosilylation

Abstract Regioselective asymmetric reduction of prochiral α,β-unsaturated ketones to optically active allylic alcohols was performed via hydrosilylation catalyzed by a rhodium(I) complex with (+)-BMPP, (+)-DIOP and (−)-DIOP as chiral ligands. The allylic alcohols with optical purity up to 69% e.e. were obtained in good yields. The extent of asymmetric induction was found to depend on the stereo-electronic matching of the chiral ligand, ketone and hydrosilane employed. In the asymmetric reduction of ( R )-carvone, leading to carveol, the extent of asymmetric induction was found to depend markedly on the ligand/rhodium ratio. Either trans -(5 R ,1 S )-carveol or cis -(5 R ,1 R )-carveol was obtained with good stereoselectivity by using (−)-DIOP or (+)-DIOP as chiral ligand, and it turned out that the chiral center present in carvone had only a slight influence on the asymmetric induction by the chiral catalysts.

Effective homogeneous hydrogenation of α-keto esters catalysed by neutral rhodium(I) complexes with phosphine ligands and application to the asymmetric synthesis of lactates

The hydrogenation of α-keto esters was found to be catalysed effectively by neutral rhodium(I) complexes with phosphine ligands, and the asymmetric hydrogenation of pyruvates was carried out using the rhodium(I) complexes with chiral diphosphines 2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane (diop), and (2S,4S)-N-t-butoxycarbonyl-4-diphenylphosphino-2-diphenylphosphinomethylpyrrolidine (bppm), in dry benzene or tetrahydrofuran to give optically active lactates (36–76% enantiomeric excess) in nearly quantitative yields.

The photochemical reaction of benzoyltrimethylsilane with organosilicon hydrides

Abstract Photolysis of benzoyltrimethylsilane in various hydrosilanes was investigated. It was found that the benzoylsilane was subjected to photoisomerization under neutral conditions to give an open-chain siloxycarbene intermediate which was inserted into the siliconhydrogen bond of hydrosilanes, yielding a new type of compounds (III). The verification of the nature of the new reaction by means of a series of competition photolyses in hydrosilanes showed that the attacking species toward hydrosilanes has nucleophilic and almost ionic character.

Reactions of hydropolysilanes with alcohols catalysed by tris(triphenylphosphine)chlororhodium

Abstract [RhCl(PPh3)3] is a very effective catalyst for the cleavage of Si-Si bonds by alcohols.