Rhodium methyl ketone synthesis

The catalytic hydrosilylation of acetophenone or t-butyl methyl ketone with diethyl-, methylphenyl- or diphenylsilane in the presence of rhodium(I) catalysts containing (R,i )-(-l-)- or (S,S)-(—)-170, followed by acid cleavage of the intermediate silyl ethers, affords the respective alcohols with optical yields of 10—42% . The synthesis of (ff)-(-l-)-l-phenylethanol from acetophenone and diethylsilane in conjunction with the catalyst derived from (S,S)-( —)-170 was the most effective reaction (equation 28). In... 

Several specialized cyclization strategies should not be dismissed. A novel rhodium acetate-mediated cyclization was employed for the first synthesis of 3-methyl-4,6-diphenylfuro[3,4-tf]is-oxazole (9) from the 5-(a-diazobenzyl)isoxazole (185) (Equation (56)). The reactive intermediate is believed to be a carbenoid species <9iCB248i>. Another strategy exploits the reactivity of 4-halo-pyrazol-5-ones (e.g., 186) with stabilized anions (e.g., cyanoacetate esters and nitriles) to afford the 4-cyanofuro[2,3-c]pyrazol-5-ones (187) and 5-aminofuro[2,3-c]pyrazoles (188) (Scheme 30) <84H(22)2523>. Also of interest is the trichloroacetonitrile cyclization of aminopyrazole ketones (189) to the pyrrolo[2,3-c]pyrazoles (190) (Equation (57)) <86S74>. The generality of this cyclization is not known. 

Various other rhodium catalysts can initiate hydroacylation reactions. Thus, the indenyl complex [075-C9H7)Rh(J72-C2H4)2] is used in intermolecular hydroacylation44. Rhodium zeolites (RhNaX and RhNaY type zeolites) act as bifunctional catalysts for the synthesis of 2-methyl-3-hexanone and 4-heptanone (1 2 ratio) from propene, carbon monoxide and hydrogen53. In this case, the ketones may be formed via hydrocarbonylation (vide supra), however, according to control experiments, rhodium-free zeolites alone catalyze ketone formation from propene and butyraldehyde53. 

This method has two limitations. Yields of ketones are low unless R is a primary alkyl, aryl, or allyl group. The rhodium reagent is expensive, even if prepared rather than purchased. However, it is attractive for synthesis of sensitive ketones, since conditions are mdd. It was used, for example, for synthesis of (S)-(+)-4-methyl-3-heptanone, the alarm pheromone of a fungus-growing ant of the genus A ffa, with complete retention of stereochemistry (equation I). 

Conjugated dienes can be selectively hydrated to ketones in the presence of cationic ruthenium complexes with bipyridyl ligands. The role of ruthenium is to catalyze the isomerization of allylic alcohols formed by the addition of water to diene. This method allows one to convert butadiene to methyl ethyl ketone in high yield [187]. Hydration of triple bonds is one of the oldest catalytic processes of organic chemistry. Though this reaction has no industrial value, it can serve as a tool of fine organic synthesis. The hydration can be catalyzed by rhodium salts under phase-transfer conditions [188]. The more exotic process of the hydrolysis of phenylacetylene to toluene and carbon monoxide catalyzed by ruthenium complex should also be mentioned [189] ... 

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