Carbonyl compounds, rhodium catalyzed

In addition, Wu and Li recently have developed an efficient rhodium-catalyzed cascade hydrostannation/conjugate addition of terminal alkynes and unsaturated carbonyl compounds in water stereoselectively (Scheme 4.5).88... 

There are two important rhodium-catalyzed transformations that are broadly used in domino processes as the primary step. The first route is the formation of keto carbenoids by treatment of diazo keto compounds with Rh11 salts. This is then followed by the generation of a 1,3-dipole by an intramolecular cyclization of the keto carbenoid onto an oxygen atom of a neighboring keto group and an inter- or intramolecular 1,3-dipolar cycloaddition. A noteworthy point here is that the insertion can also take place onto carbonyl groups of aldehydes, esters, and amides. Moreover, cycloadditions of Rh-carbenes and ring chain isomerizations will also be discussed in this section. 

The examples described so far clearly show the value of the rhodium-catalyzed carbene transfer obtained from diazo compounds onto carbonyl and imino groups. However, the scope is even broader, as the formed carbene can also undergo an ad-... 

The rhodium-catalyzed conversion of a-diazo-p-hydroxy carbonyl into P-dicarbonyl compounds (Table 23, Entries 6-8) in general seems to be preferable to the acid-catalyzed reaction because of higher yields and absence of side-reactions 37S,377). From a screening of 20 metal salts and complexes, Rh2(OAc)4, RhCl(PPh3)3, PdCl2 and CoCl2 emerged as the most efficient catalysts for the transformation of a-diazo-P-hydroxy esters into P-ketoesters 376). This reaction has become part of... 

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... 

A variety of rhodium complexes also catalyze the isomerization of allylic alcohols to saturated carbonyl compounds. RhH(CO)(PPh3)3 quantitatively isomerized methallyl alcohol to isobutylaldehyde at 70°C in trifluoroethanol (Equation (11 )).42... 

A very extensive and detailed study of the cationic rhodium(i)-catalyzed isomerization of allylic alcohols demonstrated that mono- and disubstituted allylic alcohols can be efficiently isomerized to the corresponding carbonyl compounds through the corresponding enol compounds (Scheme 20).45 The isomerization using cationic rhodium(l)... 

The ruthenium-, rhodium-, and palladium-catalyzed C-C bond formations involving C-H activation have been reviewed from the reaction types and mechanistic point of view.135-138 The activation of aromatic carbonyl compounds by transition metal catalyst undergoes ortho-alkylation through the carbometallation of unsaturated partner. This method offers an elegant way to activate C-H bond as a nucleophilic partner. The rhodium catalyst 112 has been used for the alkylation of benzophenone by vinyltrimethylsilane, affording the monoalkylated product 110 in 88% yield (Scheme 34). The formation of the dialkylated product is also observed in some cases. The ruthenium catalyst 113 has shown efficiency for such alkylation reactions, and n-methylacetophenone is transformed to the ortho-disubstituted acetophenone 111 in 97% yield without over-alkylation at the methyl substituent. 

Extensively developed by Ojima and co-workers, SiCaT and carbonylative silylcarbocyclization (CO-SiCaC) represent a rapid entry into polycyclic molecules of interest.271 For instance, the rhodium-catalyzed intramolecular SiCaT of triyne 441 afforded tricyclic compound 442 in high yield, accompanied by a small amount of cycloadduct 443 (Scheme 111).270... 

Rhodium(i) complexes are excellent catalysts for the 1,4-addition of aryl- or 1-alkenylboron, -silicon, and -tin compounds to a,/3-unsaturated carbonyl compounds. In contrast, there are few reports on the palladium(n) complex-catalyzed 1,4-addition to enones126,126a for the easy formation of C-bound enolate, which will result in /3-hydride elimination product of Heck reaction. Previously, Cacchi et al. described the palladium(n)-catalyzed Michael addition of ArHgCl or SnAr4 to enones in acidic water.127 Recently, Miyaura and co-workers reported the 1,4-addition of arylboronic acids and boroxines to a,/3-unsaturated carbonyl compounds. A cationic palladium(n) complex [Pd(dppe)(PhCN)2](SbF6)2 was found to be an excellent catalyst for this reaction (dppe = l,2-bis(diphenyl-phosphine)ethane Scheme 42).128... 

Besides rhodium catalysts, palladium complex also can catalyze the addition of aryltrialkoxysilanes to a,(3-unsaturated carbonyl compounds (ketones, aldehydes) and nitroalkenes (Scheme 60).146 The addition of equimolar amounts of SbCl3 and tetrabutylammonium fluoride (TBAF) was necessary for this reaction to proceed smoothly. The arylpalladium complex, generated by the transmetallation from a putative hypercoordinate silicon compound, was considered to be the catalytically active species. 

Hydroformylation of hetero olefins such as carbonyl compounds is not known to proceed with significant levels of efficiency, whereas the hydroformylation of olefins has been developed to a sophisticated stage. Generally, aldehydes resultant from the latter process exhibit a low propensity to undergo further hydroformylation, with the exception of some activated aldehydes. The rhodium-catalyzed hydroformylation of formaldehyde is the key step in the synthesis of ethyleneglycol from synthesis gas. Chan et al. found... 

By tethering a,p-enones with another carbonyl-containing moiety, Rrische developed rhodium-catalyzed asymmetric 1,4-addition/aldol cyclization reactions." These reactions proceed with high diastereo- and enantioselectivity, furnishing structurally complex cyclic compounds in a single step [Eqs. (3.11-3.13)]. 

The use of organosilanes for rhodium-catalyzed conjugate addition is also feasible. In 2001, Mori reported that the catalytic conjugate addition of aryl(ethyl)silanediols to a,f -unsaturated carbonyl compounds takes place in the presence of [Rh(OH)(COD)]2 in a... 

The ability to produce 1,3-dipoles, through the rhodium-catalyzed decomposition of diazo carbonyl compounds, provides unique opportunities for the accomplishment of a variety of cycloaddition reactions, in both an intra- and intermolecular sense. These transformations are often highly regio- and diastereoselective, making them extremely powerful tools for synthetic chemistry. This is exemplified in the number of applications of this chemistry to the construction of heterocyclic and natural-product ring systems. Future developments are likely to focus on the enantioselective and combinatorial variants of these reactions. 

Only a few methods are available for the synthesis of isomilnchnones, and the original techniques are summarized by Gingrich and Baum (10). Padwa and coworkers (25) provided a more recent historical account of the synthesis of isomilnchnones. The major new development is the generation of isomilnchnones using the rhodium(II)-catalyzed decomposition of a-diazo carbonyl compounds. In continuation of earlier work (28), Haddadin and Tannus (29) extended their new synthesis of isomilnchnones 51 from A(-benzoylphenylglyoxanilides (50) as illustrated in Scheme 10.6 to a series of new compounds. 

Yu and co-workers have expanded upon Ojima s work through development of an effective Rh-catalyzed protocol for the cyclization/hydrosilylation of allenyl carbonyl compounds to form silylated vinylcycloalkanols and heterocyclic alcohols.For example, reaction of tosylamide 44 (X = NTs, R = H, n= ) and triethylsilane catalyzed by Rh(acac)(GO)2 (1 mol%) under GO (10 atm) at 70 °G for 8h gave the silylated vinyl pyrrolidinol 45 (X = NTs, R = H, n= ) in 74% yield with exclusive formation of the m-diastereomer (Equation (29)). The rhodium-catalyzed reaction was also effective for the cyclization of alleneones and for the formation of carbocycles, oxygen heterocycles, and six-membered cyclic alcohols (Equation (29)). However, Rh-catalyzed cyclization/hydrosilylation of allenyl carbonyl compounds that possessed substitution on an allenyl carbon atom was not established (Equation (29)). The efficiency of the Rh-catalyzed reaction of allenyl carbonyl compounds depended strongly on GO pressure. Reactions run under 10 atm GO were more efficient than were... 

The most common oxidation states and corresponding electronic configurations of rhodium are +1 (tf8), which is usually square planar although some five coordinate complexes are known, and +3 (T) which is usually octahedral. Dimeric rhodium carboxylates are +2 (oxidation states —1 (industrial applications include rhodium-catalyzed carbonylation of methanol to acetic acid and acetic anhydride, and hydroformylation of propene to tf-butyraldehyde. Enantioselective catalytic reduction has also been demonstrated. 

Kumada and co-workers have introduced the ferrocene-based ligand BPPFOH (62) for the rhodium-catalyzed asymmetric hydrogenation of carbonyl compounds. 

Hydrosilylation of various carbonyl compounds, enones and related functional groups catalyzed by Group VIII transition metal complexes, especially phosphine-rhodium complexes, have been extensively studied1,3, and the reactions continue to serve as useful methods in organic syntheses. 

J. Adams, D. M. Spero, Rhodium(II) Catalyzed Reactions of Diazo-Carbonyl Compounds, Tetrahedron 1991, 47, 1765-1808. 

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