Rhodium-catalyzed cyclization of 1,6-enynes triggered by addition of arylboronic acids

1,6-Enynes reacted with arylboronic acids in the presence of a catalytic amount of a rhodium(I) complex under mild conditions to give (Z)-1-(1-arylethylidene)-2-vinylcyclopentanes. The regioselective addition of an arylrhodium(I) species across the carbon-carbon triple bond triggered the cyclization process. Intramolecular carborhodation onto the pendent alkene in a 5-exo mode furnished a five-membered ring. Finally, the rhodium(I) methoxide generated by beta-methoxy elimination reacted with the arylboronic acid to promote the next catalytic cycle.     

Rhodium-catalyzed arylative and alkenylative cyclization of 1,5-enynes induced by geminal carbometalation of alkynes

A rhodium(I)-catalyzed addition-cyclization of 1,5-enynes with aryl- and alkenylboronic acids has been developed. The reaction allows for efficient C-C coupling of multiple reactive components while accomplishing a net R,H-addition in a single step under mild conditions. In the presence of [Rh(OH)(COD)]2 catalyst and triethylamine base in methanol solvent, a range of 1,5-enynes undergo an intermolecular addition with a wide variety of aryl- and alkenylboronic acids and concomitant endo-selective cyclization to yield 1-aryl and alkenyl-substituted cyclopentene derivatives as the products. Deuterium labeling studies suggest that the reaction involves formation of a rhodium vinylidene complex with the terminal alkyne of the enyne substrate. The subsequent migration of the aryl or alkenyl group from the rhodium center to the alpha-carbon of the vinylidene ligand gives a vinyl rhodium complex, a formal 1,1-carbometalation process of the alkyne. This vinyl rhodium then adds to the pendent alkene, and the protodemetalation of the resulting rhodium enolate affords the product.     

Rhodium-catalyzed addition/ring-opening reaction of arylboronic acids with cyclobutanones

Cyclobutanones react with arylboronic acids in the presence of a catalytic amount of Rh(I) complex to afford butyrophenone derivatives through the addition of an arylrhodium(I) species to the carbonyl group, followed by ring-opening of the resulting rhodium(I) cyclobutanolate. [reaction: see text]     

Cationic Pd(II)-catalyzed arylative cyclization of 1,6-enynes with arylboronic acids

A cationic Pd(II)-catalyzed redox neutral arylative cyclization of enynes by using β-acetoxy elimination as the quenching step has been developed. The reaction offers an efficient method to access a variety of carbocycles and N-heterocycles bearing an exocyclic double bond.     

Rhodium-catalyzed addition of arylboronic acids to alkynyl aza-heteroaromatic compounds in water

Alkynyl heteroaromatic compounds reacted with arylboronic acids to give addition products in the presence of a rhodium catalyst. The best results were obtained when a novel pyridine-substituted water-soluble phosphine ligand was used. The reactions proceed to give trisubstituted alkenes from various arylboronic acids and alkynyl heteroaromatic compounds with high regioselectivity. Only alkynes with a nitrogen atom in proximity to the triple bond were converted to the corresponding alkenes, as expected for a chelation-controlled addition.     

Nickel salt-catalyzed addition reaction of arylboronic acids to aromatic aldehydes

Arylation reaction of aromatic aldehydes with arylboronic acids proceeded smoothly in the presence of a base and catalytic amount of a nickel salt, Ni(ClO₄)₂·6H₂O, in toluene/IPA = 5:1 or IPA to afford corresponding diarylmethanols in good to excellent yields.     

Rhodium-catalyzed asymmetric conjugate addition of arylboronic acids to nitroalkenes using olefin-sulfoxide ligands

An efficient rhodium/olefin-sulfoxide catalyzed asymmetric conjugate addition of organoboronic acids to a variety of nitroalkenes has been developed, where 2-methoxy-1-naphthyl sulfinyl functionalized olefin ligands have shown to be highly effective and are applicable to a broad scope of aryl, alkyl, and heteroaryl nitroalkenes.     

Nickel(II)-catalyzed addition reaction of arylboronic acids to isatins

A Ni-catalyzed addition of arylboronic acids to isatins was first developed. The reaction, driven by Ni(acac)₂ and dppp as the phosphine ligand, gave 3-aryl-3-hydroxy-2-oxindoles in up to 97% yield. Scopes of benzyl-protected isatins and arylboronic acids were examined. Substituted phenylboronic acids along with fused-ring and heterocyclic boronic acids reacted with isatins smoothly. Preliminary asymmetric catalysis was investigated as well, showing moderate enantioselectivity. The mechanism was also described.     

Enantioselective arylative cyclization of allenyl aldehydes with arylboronic acids under Pd(II)-diphosphine catalysis

A Pd(OAc)2-SEGPHOS combination catalyzes the first enantioselective arylative cyclization of allenyl aldehydes with arylboronic acids to provide cis-fused five- and six-membered cyclic homoallylic alcohols. The excellent diastereo- and enantioselectivity and the fact that the reaction proceeds at room temperature in the absence of any additives make the process highly practical.     

Novel hexadentate imidazolium salts in the rhodium-catalyzed addition of arylboronic acids to aldehydes

Four novel hexadentate imidazolium salts were synthesized from hexakis(bromomethyl)benzene and 1-substituted imidazole. The arylation of aldehydes with arylboronic acids was effected conveniently and in high yields by a catalyst system generated in situ from these hexadentate imidazolium salts, [Rh(COD)Cl]₂ and a base.     

Rhodium-catalyzed asymmetric hydroarylation of diphenylphosphinylallenes with arylboronic acids

Rhodium-catalyzed asymmetric hydroarylation of diphenylphosphinylallenes with arylboronic acids proceeded in high yields with high regio- and enantioselectivity to give chiral allylphosphine oxides of up to 98% ee. The structural determination of the key intermediate, a pi-allylrhodium complex, was successful to establish the catalytic cycle of the reaction.     

Rhodium-catalyzed addition of alcohols to terminal enones

[Rh(COD)(OMe)]₂ was found to catalyze the addition of aliphatic and aromatic alcohols with terminal enones to afford β-alkoxyketones in high yields.     

Rhodium-catalyzed Michael addition of arylboronic acids to 3-alkylenyloxindoles: asymmetric synthesis of functionalized oxindoles

The rhodium-catalyzed diastereo- and enantioselective Michael addition of arylboronic acids to 3-alkylenyloxindoles has been developed with (R)-binap as a ligand. A wide variety of the desired functionalized oxindoles are smoothly obtained in high yields (up to 99%) with high enantioselectivities (up to 92% ee) and good diastereoselectivities (up to 82:18).     

Rhodium-catalyzed addition of aryldifluoromethylsilanes to N-sulfonylaldimines

The addition of aryldifluoromethylsilanes to N-sulfonylaldimines was found to be catalyzed by a rhodium complex, [Rh(cod)(MeCN)₂]BF₄, in the presence of potassium fluoride to give the corresponding arylated N-sulfonylamines in good yield. The reaction mechanism would involve the generation of a fluoride-coordinated arylsilicate and the transmetalation between the arylsilicate and the rhodium complex to give the arylrhodium species as a key intermediate.     

The first examples of rhodium-catalyzed 1,4-conjugate addition reactions of arylboronic acids with ethenesulfonamides

An unprecedented rhodium-catalyzed 1,4-conjugate addition of arylboronic acids with ethenesulfonamides resulting in the corresponding 2-arylethanesulfonamides is described. The amino substituent, the applied arylboronic acid, the type of Rh-catalyst, and the experimental conditions all affected the reaction outcome.     

Cationic Pd(II)-catalyzed highly enantioselective arylative cyclization of alkyne-tethered enals or enones initiated by carbopalladation of alkynes with arylboronic acids

Cationic Pd(II)-catalyzed enantioselective arylative cyclization of alkyne-tethered enals or enones initiated by carbopalladation of alkynes was developed without the necessity of a redox system.     

Rhodium-catalyzed addition of arylboronic acids to isatins: an entry to diversity in 3-aryl-3-hydroxyoxindoles

[reaction: see text] A general method for the catalytic 1,2-addition of aryl and alkenyl boronic acids to isatins is described using a rhodium(I)/triphenylphosphite catalyst. The application of this transformation allows the synthesis of a variety of 3-aryl-3-hydroxyoxindole building blocks in high yields. An enantioselective version of this reaction using a rhodium(I)/phosphoramidite system is also presented.     

Rhodium-catalyzed enantioselective 1,4-additions of arylboronic acids to substituted enones

The rhodium-catalyzed enantioselective 1,4-addition of arylboronic acids to the bifunctional Michael acceptors 1–3 in the presence of phosphoramidites L2–L4 occurs regioselectively at the endocyclic C–C double bond and in up to 95% ee. The presence of KOH is required to increase the reactivity so that less boronic acid and lower reaction temperatures can be used. The corresponding addition to chiral enone 4 takes place with epimerization of the product to the thermodynamically more stable trans-isomer, which was obtained with up to 98% ee.     

Rhodium-catalyzed asymmetric coupling reaction of allylic ethers with arylboronic acids

An asymmetric allylic substitution of simple allylic ethers with arylboronic acids in the presence of a rhodium(I)/(R)-DTBM-SEGPHOS catalyst has been developed. The reactions proceeded smoothly at room temperature to give the corresponding branch products with excellent regioselectivities and good to excellent enantioselectivities.