Rhodium catalyzed arylboronic acid

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. 

Scheme 1.16 Rhodium(l) catalyzed arylboronic acid diastereoselective addition.

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... 

Rhodium-catalyzed Heck-type coupling of boronic acids with activated alkenes was carried out in an aqueous emulsion.82 The couplings between arylboronic acids and activated alkenes catalyzed by a water-soluble tm-butyl amphosrhodium complex were found to progress at room temperature to generate Heck-type products with high yields and excellent selectivity. It was necessary to add two equivalents of the... 

Trost reported the synthesis of 1,4-dienes with ruthenium catalysis through regioselective carbometallation of alkynes with alkenes.51 Di- and trisubstituted olefins can also be obtained with arylboronic acids through an intermolecular process under rhodium,30 52 55 nickel,56 and palladium catalysis.57 Recently, Larock has reported an efficient palladium-catalyzed route for the preparation of tetrasubstituted olefins.58,59... 

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). 

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... 

Arylative cyclization of alkynals with arylboronic acids is catalyzed by rhodium-diene complexes and even proceeds enantioselectively in the presence of a chiral diene (Equation (48)).399... 

Simiraly, alkynones undergo arylative cyclization with arylboronic acids in the presence of a rhodium catalyst (Equation (49)).400 When acetylenic /3-keto esters are employed as shown in Equation (50), arylative cyclization (formation of cyclobutanols) and subsequent, facile acid-catalyzed bond cleavage take place to give <5-keto esters.401 Ring expansions of cyclic [3-keto esters are also possible according to this reaction. 

Following the initial work by Hayashi and Miyaura using (5)-binap, several other chiral ligands were reported to achieve high enantioselectivity in the rhodium-catalyzed asymmetric 1,4-addition of arylboronic acids to ot,p-enones (Figure 3.18). A polymer-supported (X)-binap analog 42 was also synthesized and it was successfully utilized in the rhodium-catalyzed asymmetric 1,4-addition reactions in water (Figure 3.19)." The stereoselectivities observed in this system are comparable to those obtained in the unsupported Rh/(5)-binap system. It was also... 

Figure 3.18. Chiral ligands that exhibit high enantioselectivity in the rhodium-catalyzed 1,4-addition of arylboronic acids to a,P-enones.

Murakami [27] and Lautens [28] independently reported the rhodium-catalyzed addition of arylboronic acids to oxanorbornenes (Scheme 3.12). Murakami reported that the reaction of oxabenzonorbornadiene 37 a with phenylboronic acid 2m, in the presence of a rhodium-P(OEt)3 catalyst in MeOH at reflux, gave an 86% yield of the ring-opened alcohol 38 am. Lautens reported the asymmetric version of the reaction, where high enantioselectivity was observed with chiral ferrocenylbisphosphine hgand 39 in a... 

A rhodium-chiral phosphine complex catalyzes the enantioselective addition of phenylboronic acid to 1-naphthaldehyde to give a chiral diaryl carbinol but with moderate ee (Scheme 13) [39]. When considering the introduction of functionalized aryl groups, arylboronic acid is a promising alternative arylating reagent to diarylzinc compounds. 

An asymmetric 1,4-addition of arylboronic acids to coumarins such as 220 catalyzed by rhodium has been achieved in greater than 99% ee (Equation 21) <2005OL2285>. This method should prove useful for the synthesis of enantiomerically enriched compounds that contain a stereogenic center between two aryl groups. This methodology was used in the total synthesis of (R)-tolterodine. 

These monodentate ligands, containing very bulky chiral N-substituents, have been applied in the asymmetric rhodium(I)-catalyzed conjugate addition of arylboronic acids to a-enones (Scheme 38) originally developed by Miyaura, Hayashi and coworkers [98]. 

Arylmetallic reagents other than arylboronic acid were shown to be applicable in the rhodium-BINAP-catalyzed arylation. Aryltitanium reagent 93 con-... 

Arylboronic acids added to alkynes975-977 and activated alkenes such as norbornene978-981 or 2-vinylpyridines982 in the presence of a rhodium(i) catalyst. Addition of arylboronic acids to allenes was reported to be catalyzed by Pd(PPh3)4 in the presence of AcOH.983... 

Certain pyrones react with active hydrogen compounds in a quite different way they display their alkenic character by participating in Michael reactions, thus coumarin itself gives 316 with malonate anion, and coumarins 317 react with arylboronic acids catalyzed by rhodium giving 318 in greater than 99% ee <2005OL2285>. 

Catalytic, Enantioselective Addition of Arylboronic Acids to Cycloalkenones. A complex between ligand 1 and a rhodium(I) salt was found to catalyze the asymmetric 1,4-addition reaction of arylboronic acids to cyclohexenone and cyclohep-tenone. The reaction proceeds with high enantiocontrol and excellent yields (eq 4). Lower enantiomeric excesses were observed with cyclopentenone (83% ee), but a variety of substituted phenyl-boronic acids could be used. 

In some cases, it is possible to couple an alcohol with an organometallic compound. Allylic alcohols are coupled with alkylmagnesium bromides in the presence of Ti(OiPr)4, for example. Allylic alcohols can be coupled with arylboronic acids in ionic liquid solvent and a rhodium catalyst. The palladium-catalyzed... 

Hayashi. T.. Inoue. K.. Taniguchi, N., and Ogasawara, M., Rhodium-catalyzed hydroarylation of alkynes with arylboronic acids. 1,4-Shift of rhodium from 2-ai yl-l-alkcnylrhodium to 2-alkenylaryl-rhodium intermediate. 7. Am. Chem. Soc., 123, 9918, 2001. 

Imines derived from N tert butanesulfinamide also undergo diastereoselective rhodium(I) catalyzed addition of arylboronic acids [61] (Scheme 1.16), a reaction that has been primarily developed for catalytic asymmetric processes (see below). 

Alternatively, it is also possible to use in situ generated N Boc imines as electro philes [117]. When a carbamoyl sulfones are treated under the rhodium catalyzed addition of arylboronic acids, the imine is formed in situ, and the nucleophilic addition proceeds smoothly to generate the N Boc protected amine (Scheme 1.34). 

Zhang L, Wu J (2008) Rhodium/N-heterocyclic carbene-catalyzed cross-couplings of aryl arenesulfonates with arylboronic acids. Adv Synth Catal 350 2409-2413 See also [124]... 

Additionally, the efficient synthesis of substituted phenylalanine-type amino acids using a rhodium catalyzed, conjugate addition of arylboronic acids has been described. The reactions are run in water using a low loading (0.5 mol%) of the rhodium catalyst [28]. 

Zou, G., Wang, Z., Zhu, J. and Tang, J. (2003) Rhodium-catalyzed Heck-type reaction of arylboronic acids with a,/3-unsaturated esters tuning /3-hydrogen elimination versus hydrolysis of alkylrhodium species. Chem. Commun., 2438-9. 

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