Rhodium ketone arylation

In addition to aryl halides and triflates, organometallic reagents can be utilized for the catalytic arylation reaction. The rhodium-catalyzed arylation of arylpyridines proceeds with the use of tetraarylstannanes (Equation (67)).83 The ruthenium-catalyzed reaction of aromatic ketones with arylboronates affords the ortho-arylated aromatic ketones (Equation (68)).84... 

Activity of the Wilkinson catalyst [RhCUPPhsls] in hydrosilylation of carbonyl compounds was already reported by Ojima and co-workers in 1972 (201). The catalyst is highly active in the hydrosilylation of a variety of diaryl, aryl alkyl, and dialkyl ketones, aryl and alkyl aldehydes, a,jS-unsaturated ketones, and esters. Stereoselectivity of hydrosilylation of cyclic ketones depends onbuUd-ness and electronic nature of silanes used. The hydrosilylation of a,/9-unsaturated carbonyl compounds in the presence of [RhCKPPhsls] and other rhodium complexes shows a specific dependence of l,2-/l,4-addition selectivity on the nature of the silane used so that monohydrosilanes undergo 1,4-addition whereas di- and trihydrosilanes give selectively 1,2-addition product (Scheme 29). 

Rhodium-catalyzed arylative ring-opening/spiroannulation of (3-arylcyclo-butylidene)acetate 23 with NaBPh, involved one C-C bond cleavage, two C-H bond cleavages, and three C-C bond formations to afford ketone 24 possessing a l,l -spirobiindane skeleton (Scheme 3.8) [20]. 

Rhodium-catalyzed arylation of 2-(2-alkynylphenyl)cyclobutanone 39 proceeded with site-selective P-carbon elimination of the benzylic carbon to afford the seven-membered ring ketone 40 (Scheme 3.19) [31]. 

Secondary benzylic alcohols are often oxidized to the corresponding ketones under the palladium-catalyzed arylation conditions. In contrast, a unique rhodium-catalyzed arylation of diarylmethanols having a 2-(2-pyridiyl) moiety... 

The benzylic position of an alkylbcnzene can be brominated by reaction with jV-bromosuccinimide, and the entire side chain can be degraded to a carboxyl group by oxidation with aqueous KMnCfy Although aromatic rings are less reactive than isolated alkene double bonds, they can be reduced to cyclohexanes by hydrogenation over a platinum or rhodium catalyst. In addition, aryl alkyl ketones are reduced to alkylbenzenes by hydrogenation over a platinum catalyst. 

Chiral diamino carbene complexes of rhodium have been merely used in asymmetric hydrosilylations of prochiral ketones but also in asymmetric addition of aryl boron reagents to enones. 

Another approach in the use of chiral S/P ligands for the hydrosilylation reaction of ketones was proposed more recently by Evans et Thus, in 2003, these workers studied the application of new chiral thioether-phosphinite ligands to enantioselective rhodium-catalysed ketone hydrosilylation processes. For a wide variety of ketones, such as acyclic aryl alkyl and dialkyl ketones as well as cyclic aryl alkyl ketones and also cyclic keto esters, the reaction gave high levels of enantioselectivity of up to 99% ee (Scheme 10.44). 

The combination of [Rh(Cl(NBD)]2 and ligands 89, 90, 91, or 92 with diphenylsilane asymmetrically reduces aryl alkyl ketones, including acetophenones, in excellent yields and in 81 to 90% ee (Eq. 346).574 The best results are with ferrocene 91 and acetophenone in toluene.575 Other phosphine-substituted ferrocenes do not give comparable results. Rhodium(I) complexes of TADDOL-derived... 

The PennPhos ligands, for example 108, complexed with rhodium, provide an excellent system for the hydrogenation of aryl alkyl ketones with ee values in the range of 94-96% (Eq. 362). Phenyl isopropyl ketone shows only a 72% ee under similar conditions. Dialkyl ketones exhibit ee values in the range of 73-94% with this system (Eq. 363).640... 

The rhodium cyclopentadienyl complex [T75-C5(CH3)5RhCl2]2, in the presence of base at 50 atm H2, also effects stereoselective catalytic hydrogenation of benzenes. Substrates with unprotected —OH or —C02H groups were not effectively hydrogenated, but aryl ethers, esters, and ketones and N,iV -dimethylaniline were all reduced, some-... 

Ruthenium- and rhodium-catalyzed reactions lead to aryl ketones, and in some cases these processes are reversible (Equations (112) and (113)).103... 

The first example of asymmetric rhodium-catalyzed 1,4-addition of organoboron reagents to enones was described in 1998 by Hayashi and Miyaura. Significant progress has been made in the past few years. This asymmetric addition reaction can be carried out in aqueous solvent for a broad range of substrates, such as a,/ -unsaturated ketones, esters, amides, phosphonates, nitroalkenes. The enantioselectivity is always very high (in most cases over 90% ee). This asymmetric transformation provides the best method for the enantioselective introduction of aryl and alkenyl groups to the / -position of these electron-deficient olefins. 

In 1997, Miyaura and co-workers reported the nonasymmetric version of 1,4-addition of aryl- and alkenylboronic acids to a,/ -unsaturated ketones using rhodium-phosphine complex as the catalyst.97 Later, Hayashi and Miyaura realized the asymmetric 1,4-addition with high catalytic activity and enantioselectivity.98 In the presence of ( y)-BINAP, the reaction of 2-cyclohexenone with 2.5 equiv. of phenylboronic acid gave (A)-3-phenylcyclohexanone with 97% ee (BINAP = 2,2 -bis (diphenylphosphino)-l,l -binaphthyl Scheme 29).99... 

Reactions of aryl- and styrylboronic acids with acid anhydrides are catalyzed by rhodium complexes to give ketones... 

Recently, the first report was made on the ruthenium-catalyzed enantioselective hydrogenation of aryl-methyl ketones using monodentate phosphonites (Scheme 28.18). In particular, ligand 15f induced excellent ee-values. One very early report on rhodium-catalyzed hydrogenation of ketones using the monophosphine bmpp 1 f met with a low e.e. [95]. 

Fluorosilylsubstituted aryl derivatives were found to be useful reagents for carbon-carbon bond formation via palladium-catalyzed cross-coupling with aryl halides in the presence of fluoride anions as Si—C bond activator in dimethylformamide (DMF), as well as rhodium-catalyzed 1,4-addition to a, 3-unsaturated ketones in the presence of a fluoride anion source (Equation 14.11) [66, 69, 70],... 

Addition of Organometallic Reagents to Enones in Aqueous Media Rhodium-catalyzed 1,4-addition of organometallic reagents to a,p-unsaturated compounds was first developed by Miyaura in 1997. Thus, Rh(acac)(CO)2/dppb was found to catalyze the 1,4-addition of aryl- and alkenylboronic acids to several ot,(3-unsaturated ketones in water-containing solvents at 50°C. The reaction conditions were successfully modified for the development of an asymmetric variant of this process by Hayashi and Miyaura in 1998. The important points of modification are (1) the use of Rh(acac)(C2H4)2/(5)-binap as a catalyst and... 

Oi and Inoue recently described the asymmetric rhodium-catalyzed addition of organosilanes [35]. The addition of aryl- and alkenyltriaUcoxysilanes to u,y9-unsaturated ketones takes place, in the presence of 4 mol% of a cationic rhodium catalyst generated from [Rh(COD)(MeCN)2]BF4 and (S)-B1NAP in dioxane/H20 (10 1) at 90°C, to give the corresponding conjugate addition products (Eq. 3). The enantioselectivity is comparable to that observed with the boronic acids, as the same stereochemical pathway is applicable to these reactions (compare Scheme 3.7). 

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