Aryl ketones, silane reduction

The quininium and quinidinium fluoride catalysts, 10 (R=H etc., X=F) and 8 (R=H, X=F), were used for the asymmetric reduction of alkyl aryl ketones in conjunction with silanes.1751 One of the most efficient silanes proved to be tris(trimethylsiloxy)silane, which together with 8 (R=H, X=F) reduced acetophenone to give the alcohol 102 in almost quantitative yield with 78 % ee, as shown in Scheme 31. The... 

Reductions. In contrast to hydrosilylation reactions catalyzed by metal chlorides, aldehydes and ketones are rapidly reduced at rt by Triethylsilane and BF3-OEt2, primarily to symmetrical ethers and borate esters, respectively. Aryl ketones like acetophenone and benzophenone are converted to ethylbenzene and diphenyl-methane, respectively. Friedel-Crafts acylation-silane reduction reactions can also occur in one step using these reagents thus Benzoyl Chloride reacts with benzene, triethylsilane, and BF3-OEt2 to give diphenyhnethane in 30% yield. ... 

Reduction of aryl alkyl ketones with moderate to good (ee 30-80%) entantio-selectivity has been achieved using trialkoxysilanes in the presence of chiral quininium fluorides (or hydroxides) [20]. Greater selectivities were noted (ee >65%) when tris(trimethylsiloxy)silane was used. 

Reduction The asymmetric reduction of a series of aryl alkyl ketones with quaternary ammonium fluorides and silanes was reported by Drew and Lawrence [55]. In these reactions, the best catalysts (e.g., 6f) were from the qui ni ne/quinidine series in fact, a fluoride salt prepared from cinchonine gave no induction. The use of trimethoxysilane resulted in faster rates but lower enantioselectivites when compared with tris(trimethoxy)silane. It is interesting that, with the... 

The asymmetric organocatalytic transformation of a ketone into an alcohol may be realized with the combination achiral silanexhiral phase-transfer catalyst, such a quaternary ammonium salt. The final alcohol is then recovered by an additional hydrolytic step. The asymmetric reduction of aryl alkyl ketones with silanes has been reported (ee-values up to 70%), the catalysts utilized being ammonium fluorides prepared from the quinine/quinidine series (e.g., 18 in Scheme 11.6) [19]. (For experimental details see Chapter 14.21.1). The more appropriated silanes were (Me3SiO)3SiH or (MeO)3SiH (some examples are... 

Nickel-catalyzed ketone and aldehyde hydrosilylations have been developed with well-defined Ni(II) hydrides using phosphine anilide ligands (Scheme 3-84). This process is tolerant of a variety of functional groups including aryl halides. In mechanistically distinct processes, nickel(O) complexes of NHCs were shown to catalyze ketone hydrosilylations using carbohydrate-derived silanes in a process that allows reductive glycosylations of ketones. Chemoselectivity of the latter method was optimal in the presence of Ti(OR)4 additives. 

Cyclometalation has been applied to synthesis in the Murai reaction. The substrate has to contain a group, a ketone in Eq. 14.42, that binds the metal complex. Cyclometalation gives an intermediate aryl that undergoes insertion with a vinyl silane followed by reductive elimination to give the product the result is a C-H addition across a C=C bond. ... 

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