Rhodium catalyzed decarbonylations

In addition to Pd-catalyzed decarbonylation, rhodium complexes catalyze the decarbonylation efficiently. In this section, decarbonylation of acyl halides and aldehydes using palladium catalysts is surveyed. ... 

Increasing use is being made of pyran syntheses based upon [4 + 2] cycloadditions of carbonyl compounds. The appropriate unsaturated aldehyde with ethyl vinyl ether yields 53 with peracids this affords an epoxide that undergoes ring contraction to the aldehyde 54 (Scheme 23) and rhodium catalyzed decarbonylation affords the required 3-alkylfuran with the optical center intact.116 Acetoxybutadiene derivatives add active carbonyl compounds giving pyrans that contract under the influence of acids to give... 

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... 

The major drawback in the development of efficient catalytic PK protocols is the use of carbon monoxide. Many groups probably refuse to use this reaction in their synthetic plans in order to avoid the manipulation of such a highly toxic gas. Carbonylation reactions without the use of carbon monoxide would make them more desirable and would lead to further advances in those areas. Once the use of rhodium complexes was introduced in catalytic PKR, two independent groups realized these species were known for effecting decarbonylation reactions in aldehydes, which is a way to synthesize metal carbonyls. Thus, aldehydes could be used as a source of CO for the PKR. This elegant approach begins with decarbonylation of an aldehyde and transfer of the CO to the enyne catalyzed by rhodium, ruthenium or iridium complexes under argon atmosphere (Scheme 36). 

Fristrup P, Kreis M, Pahnelund A, Norrby PO, Madsen R (2008) The mechanism for the rhodium-catalyzed decarbonylation of aldehydes a combined experimental and theoretical study. J Am Chem Soc 130 5206-5215... 

Kaneda, K., Azuma, H., Wayaku, M., Teranishi, S. Decarbonylation of a- and 3-diketones catalyzed by rhodium compounds. Chem. Lett. 1974, 215-216. 

Oxidative addition of aldehydes is expected from the mechanism of their decarbonylation reactions, catalyzed by rhodium and palladium catalysts 9-10>. Harvie and Kemmitt reported the formation of the following diacyl complex by the reactions of the aldehydes with Pt(PPh3)4 u). 

In the foregoing, the formation of organic molecules on transition metal complexes is explained by stepwise processes of oxidative addition, insertion, and reductive elimination. One typical example, which can be clearly explained in this way, are the carbonylation and decarbonylation reactions catalyzed by rhodium complexes 10-137). Tsuji and Ohno found that RhCl(PPh3)3 decarbonylates aldehydes and acyl halides under mild conditions stoichiometrically. Also this complex and RhCl(CO) (PPh3)2 are active for the catalytic decarbonylation at high temperature. 

Because decarbonylation of the acyl intermediate competes with olefin insertion into the same species, and the carbonyl complexes are inactive as catalysts, the catalyst is poisoned by the competing decarbonylation. The use of a cationic rhodium complex containing a chelating ligand suppresses poisoning of the catalyst by decarbonylation, and reactions of aIk-4-en-l-als catalyzed by rhodium complexes of bisphosphines formed the desired cyclo-pentanones faster than reactions catalyzed by neutral rhodium complexes. "... 

In contrast to a number of studies on the homogeneous hydrogenation of carbon-carbon multiple bonds [25], there had been few papers about hydrogenation of simple ketones before Schrock and Osborn [26] reported in 1970 a catalytic activity of cationic rhodium complexes with relatively basic phosphines as ligands. In fact, the Wilkinson s rhodium(I) complex usually lacks activity towards hydrogenation of carbonyl groups, and rather catalyzes decarbonylation of aldehydes. The catalytic cycle of the hydrogenation of ketones proposed by Schrock and Osborn is depicted in Scheme 3. 

SCHEME 22.5 Decarbonylative coupling of aromatic aldehydes and norbomenes catalyzed by rhodium. 

A related approach involves the direct decarbonylation of stable ketones. DauguUs and Brookhart demonstrated that the rhodium-catalyzed decarbonylation of diaryl ketones was feasible [11]. Efficient extrusion of CO from alkyl aryl ketones to form alkylarenes was easily achieved by rhodium(I) catalysis directed by apyridyl ortho to the RCO group (Scheme 22.6) [12]. (CO)2Rh(acac) was found to be the optimal catalyst and the methodology had a broad substrate scope. This method offers an alternative way to synthesize alkyl benzenes through an ARCIS reaction, complementary to the known Friedel-Crafts alkylation reaction of arenes. 

Yang, L., Guo, X., Li, C.-J. (2010). The first decarbonylative coupling of aldehydes and norbwnenes catalyzed by rhodium. Advanced Synthesis and Catalysis, 352, 2899-2904. 

Maetani, S., Fukuyama, X, Ryu, I. (2013). Rhodium-catalyzed decarbonylative C-H arylation of 2-aryloxybenzoic acids leading to dibenzofuran derivatives. Organic Letters, 15, 2754-2151. 

Scheme 8.2 Rhodium-catalyzed decarbonylation of an a,(i-unsaturated aldehyde.

Scheme 8.4 Rhodium-catalyzed decarbonylation of heptanal with rhodium complexes bearing chelating diphosphine ligands.

Scheme 8.6 Side products in the rhodium-catalyzed decarbonylation of pent-4-enal in hs presence of ethylene.

Scheme 8.8 Rhodium-catalyzed decarbonylation of 3-methyl-3-phenylbutanal.

Scheme 8.11 Rhodium(triphos)-catalyzed decarbonylation of aldehydes.

Scheme 8.13 Rhodium-catalyzed decarbonylation of an aldehyde derived from a Diels-Alder reaction.

An intramolecular version of decarbonylative annulation was catalyzed by rhodium(l) - PPhj catalysts to provide bicyclic cyclopentenones (Scheme 3.55) [64]. 

The first example that we discuss is the rhodium-catalyzed decarbonylation of aldehydes. This reaction was investigated owing to its potential in the conversion of biomass into chemicals or fuel as this contributes to the reduction of the oxygen content, which is one of the major challenges in biomass utilization [46]. 

Recently, Tang and coworkers [246] reported a new method for the formation of conjugated hb polymers with diyne monomer [bis(4-ethynylphenyl)dimethylsilane] and benzene-1,3,5-tricarbonyl trichloride as branching unit using the A2-1- B3 polymerization approach (Table 5, entry 2) by the rhodium (Rh)-catalyzed decarbonylative reaction for the formation of hb poly(arylene chloro-vinylene)s. The molar ratio selected for polymerization of A2 B3 was 4 3 (A B = 8 9) so as to... 

However, the decarbonylation reaction can be suppressed by the use of specially tailored chelating groups. Intermolecular processes involving dienes and salicylaldehydes are now known, and are thought to proceed via a double chelation mechanism, akin to the Jun-type system. Rhodium-catalyzed reactions lead to hydroacylated products, under relatively mild conditions (Equation (134)).117... 

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