Arylboronic acids addition

Rhodium Diene-Catalyzed Arylation of Imines Hayashi has shown that the asymmetric synthesis of diarylmethylamines could be realized with high enantio control by the rhodium catalyzed arylboronic acid addition to N tosyl imines [119]. Ihe rhodium catalyst bears the C2 symmetrical bicyclo 2.2.1]heptadicne ligand 54. 

Jeletic MS, Lowry RJ, Swails JM, Ghiviriga J, Veige AS. Synthesis and characterization of kappa-2-bis-N-heterocyclic carbene rhodium(I) catalysts application in enantioselective arylboronic acid addition to cyclohex-2-enones. J Organomet Chem. 2011 696 3127-3134. 

Arylboronic acids have traditionally been prepared via the addition of an organomagnesium or organolithium intermediate to a trialkyl borate. Subsequent acidic hydrolysis produces the free arylboronic acid. This limits the type of arylboronic acids one can access via this method, as many functional groups are not compatible with the conditions necessary to generate the required organometallic species, or these species may not be stable intermediates. 

The optimal reaction conditions were applied with 59d in the addition of various aryl boronic acids and potassium trifluoroborates to several cyclic and acyclic enones (Fig. 8). Arylboronic acids added to cyclic enones in high yields (89-97%) and with good to excellent selectivities (85-98% ee). Under these conditions, the potassium trifluoroborate reagents reacted at faster rates, but with slightly lower selectivities (83-96% ee). The reactions of acyclic enones with aryl boron reagents gave also excellent yields (83-96%). 

The facile arylation of aldehydes with arylboronic acid has prompted the exploration of asymmetric versions of this reaction. However, this field has been scarcely explored and only few examples have been reported in the literature, with moderate results. The first diastereoselective example was described by Ftirstner and coworkers. By reacting the Gamer aldehyde 15 with phenylboronic acid under their set of experimental conditions (i.e. RhClj-SH O, IPr HCl) (Scheme 7.4) [21], the secondary alcohol was obtained in higher selectivity than that observed in the addition of phenylmagnesium bromide reported by Joullie (de = 94% versus 66%), with the anti isomer as the major compound [29]. 

Scheme 2.34 Rh-catalysed 1,4-additions of arylboronic acids to cyclic enones with bis(sulfoxides) ligand.

Arylation of alkynes via addition of arylboronic acids to alkynes represents an attractive strategy in organic synthesis. The first addition of arylboronic acids to alkynes in aqueous media catalyzed by rhodium was reported by Hayashi et al.89 They found that rhodium catalysts associated with chelating bisphosphine ligands, such as 1,4-Ws(diphenyl-phosphino)butane (dppb) and 1,1 -/ E(diphenylphospliino)fcrroccnc... 

Biphasic systems were found to have a unique effect on the selectivity of the addition of arylboronic acids to alkynes. It was found that the use of [Rh(COD)OH]2 associated with the water-soluble ligand, m-TPPTC, was highly effective for such a reaction in the biphasic water/toluene system (Eq. 4.51).91 The reaction was completely stereo-and regioselective. In addition, the catalyst did not lose any activity... 

Bidentate ligands with very wide bite angles (like dpephos or xantphos, Scheme 4) are likely to form unstable chelates prone to dechelation at elevated temperatures, thus giving another route to monophosphine species. The application of such ligands to the crosscoupling of sterically hindered bromides and arylboronic acids under strictly anhydrous conditions enforced by the addition of molecular sieves has been shown to be advantageous (118).398... 

Cationic palladium-catalyzed addition of arylboronic acids to nitriles for the formation... 

A very recent addition to the already powerful spectrum of microwave Heck chemistry has been the development of a general procedure for carrying out oxidative Heck couplings, that is, the palladium)11)-catalyzed carbon-carbon coupling of arylboronic acids with alkenes using copper(II) acetate as a reoxidant [25], In a 2003 publication (Scheme 6.6), Larhed and coworkers utilized lithium acetate as a base and the polar and aprotic N,N-dimethylformamide as solvent. The coupling... 

The same research group additionally presented further investigations on fluor-ous-phase palladium-catalyzed carbon-carbon couplings [93]. Fluorinated aryl octyl-sulfonates were reacted in slight excess with arylboronic acids under microwave con-... 

Vinyl- or arylboronic acids also react with allenes, affording 1,3-dienes or styrene derivatives, respectively.89 This palladium-catalyzed addition proceeds with good regioselectivity and high stereoselectivity in favor of the formation of (ft)-trisubstituted isomer. 

Very recently, Murakami has published an Rh(i)-catalyzed cyclization of 1,6-enynes triggered by addition of arylboronic acids (Scheme 74).281 Initial carborhodation of the alkyne moiety is followed by insertion into the alkene moiety. /3-Alkoxy elimination provides the final product 289 in good yield and regenerates the catalyst species. 

A broad substrate scope for the rhodium-catalyzed asymmetric 1,4-addition has been observed.98 Both arylboronic acids with either electron-donating or electron-withdrawing aryl substituents and alkenylboronic acids can be introduced into acyclic or cyclic enones with high enantioselectivities (Scheme 30). 

In 2001, Miyaura and Sakuma reported the asymmetric addition of arylboronic acids to a,/3-unsaturated amides in the presence of the Rh(acac)(C2H4)2/(V)-BINAP catalyst (acac = acetylacetonate Scheme 36).112 The... 

Recently considerable attention has been given to chiral 72-bonded olefin spectator ligands for the asymmetric conjugate addition.122 Hayashi and Carreira independently reported that new chiral diene ligands 83,123 84,124 and 85125 showed high enantioselectivities in Rh(i)-catalyzed conjugate addition of arylboronic acids to enones (Scheme 41). 

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... 

Addition of arylboronic acids to aldehydes using recoverable, water-soluble rhodium catalysts has also been reported.396... 

Cyclobutanones react with arylboronic acids to afford butyrophenones (Equation (60)). Addition of arylrhodium species to the carbonyl group followed by /3-carbon elimination is proposed. 

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