Aldehydes rhodium-catalyzed 1,2-addition

In 2005, Bolm and coworkers disclosed a new planar-chiral imidazolium salt 30 incorporating a chiral Al-substituent (Scheme 3.16) [35]. Its apphcation in rhodium-catalyzed additions of arylboronic acids to aromatic aldehydes was demonstrated, and the corresponding diarylmethanols were obtained with up to 38% ee. Since the hgand bears two chiral elements, match and mismatch effects were observed by showing that NHC 31, which is the diastereomer of 30, did not give any enantioinduction. 

The rhodium-catalyzed addition of aryl- and 1-alkenylboronic acids tooc, unsaiurated ketones, aldehydes, esters, and amides gave the conjugate 1,4-addition products in high yidds. The ifaodium(I) complexes also catalyzed the 1,2-addition of organoboronic acids to aldehydes or N-sulfonyl aldimines. The dficiency of protocol was demonstrated in the asymmetric addition reactions of organoboronic acids in the presoice of a rhodium(acacV BINAP complex. 

Scheme 7.3 Rhodium-catalyzed addition of arylboronic acids to aldehydes, as described by Furstner and Krause [5].

Scheme4.33 Other conditions for the rhodium-catalyzed addition of organoboronic acids to aldehydes.

Miyaura also [50] reported rhodium-catalyzed additions of arylboronic acids to aldimines. Despite the potential production of water from boronic adds by cydic trimerization, no hydrolysis of N-sulfonyl aldimines was observed when boronic acids were used in the rhodium-catalyzed addition to aldimines in anhydrous diox-ane. The reactions proceeded well, regardless of the presence of both an electron-withdrawing and an electron-donating group on the aldehyde or the arylboronic add. For example, the reaction of N-sulfonyl aldimine 79a with boronic acid 2o catalyzed by cationic rhodium [Rh(cod) MeCN)2]BF4 gave 87% yield of the product 80ao, and... 

Complex preparation Tandem catalysis access to ketones from aldehydes and arylboronic acids via rhodium-catalyzed addition/oxidation, (52%) [1628]. 

The use of MOPs in catalysis which resulted in low/moderate enantioselectivities Sakai M, Ueda M, Miyaura N (1998) Rhodium-catalyzed addition of organoboronic acids to aldehydes. Angew Chem Int Ed 37 3279-3281... 

Rhodium(II) acetate catalyzes C—H insertion, olefin addition, heteroatom-H insertion, and ylide formation of a-diazocarbonyls via a rhodium carbenoid species (144—147). Intramolecular cyclopentane formation via C—H insertion occurs with retention of stereochemistry (143). Chiral rhodium (TT) carboxamides catalyze enantioselective cyclopropanation and intramolecular C—N insertions of CC-diazoketones (148). Other reactions catalyzed by rhodium complexes include double-bond migration (140), hydrogenation of aromatic aldehydes and ketones to hydrocarbons (150), homologation of esters (151), carbonylation of formaldehyde (152) and amines (140), reductive carbonylation of dimethyl ether or methyl acetate to 1,1-diacetoxy ethane (153), decarbonylation of aldehydes (140), water gas shift reaction (69,154), C—C skeletal rearrangements (132,140), oxidation of olefins to ketones (155) and aldehydes (156), and oxidation of substituted anthracenes to anthraquinones (157). Rhodium-catalyzed hydrosilation of olefins, alkynes, carbonyls, alcohols, and imines is facile and may also be accomplished enantioselectively (140). Rhodium complexes are moderately active alkene and alkyne polymerization catalysts (140). In some cases polymer-supported versions of homogeneous rhodium catalysts have improved activity, compared to their homogenous counterparts. This is the case for the conversion of alkenes direcdy to alcohols under oxo conditions by rhodium—amine polymer catalysts... 

Hydroformylation, also known as the oxo process, is the transition metal catalyzed conversion of olefins into aldehydes by the addition of synthesis gas (H2/CO) and is the second largest homogeneous process in the world in which more than 12 billion pounds of aldehydes are produced each year.222 Aldehydes are important intermediates in a variety of processes such as the production of alcohols, lubricants, detergents, and plasticizers. Several transition metals can catalyze the hydroformylation of olefins, but rhodium and cobalt have been used extensively. 

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