Carbon rhodium-catalyzed conjugate addition

Hayashi and Miyaura pioneered the enantioselective rhodium-catalyzed conjugate addition of arylboronic acids to a variety of Michael acceptors a,P-unsaturated ketones, esters, lactones, amides, and lactams [215]. Generally, water is used as a cosolvent and plays a key role in the catalytic cycle, illustrated in Scheme 5.111 (cycle A) for the conjugate addition of phenylboronic acid to cyclohexenone that, when catalyzed by the Rh(I)-(S)-BINAP complex, leads to 3-phenylcyclohexanone in 97% ee and 93% chemical yield [205a]. The key intermediates of the catalytic cycle, the hydroxorhodium complex 433, the phenylrhodium complex 434, and -bound rhodium enolate 435 were characterized by NMR spectroscopy. The reaction of the hydrorhodium complex 433 with phenylboronic acid leads to a transmetallation to give the phenylrhodium complex 434. Then, the insertion of the carbon-carbon double bond of cyclohexenone into the phenylrhodium bond leads to the formation of the... 

Rhodium-catalyzed asymmetric conjugate addition has enjoyed uninterrupted prosperity since the first report by Hayashi and Miyaura [6]. Its high enantioselectivity and wide applicability are truly remarkable. However, some problems still remain, since the carbon atoms that can be successfully introduced by this rhodium-catalyzed reaction have been limited to sp carbons and the substrates employed have been limited mostly to the electron-deficient olefins free from sterically bulky substituents at a- and / -positions. These issues will be the subject of increasing attention in the future. 

The in situ generation of carbon nucleophiles via extrusion of CO2 from benzoates cannot only be combined with cross-coupling processes but also with 1,2- and 1,4-addition reactions. An example is the rhodium-catalyzed decarboxylative conjugate addition of activated benzoic acids to acrylic esters or amides developed by Zhao et al. (Scheme 19, right side) [65]. A nice application is the decarboxylative addition of aromatic carboxylic acids to nitriles in the presence of... 

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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