Ruthenium-catalyzed reaction of alkenyl triflates with zinc thiolates

A ruthenium complex coordinated with 3,4,7,8-tetramethyl-1,10-phenanthroline catalyzed the reaction of alkenyl triflates with zinc dithiolates to give alkenyl sulfides.     

Manganese-catalyzed cross-coupling reaction between aryl Grignard reagents and alkenyl halides

Aryl Grignard reagents react stereospecifically with alkenyl halides in the presence of manganese chloride (10%) to afford good yields of cross-coupling products.     

Cross-coupling reactions of (1-fluorovinyl)methydiphenylsilane(1) with aryl halides and aryl triflates

The cesium fluoride (CsF)-assisted cross-coupling reaction of (1-fluorovinyl)methyldiphenylsilane (1) with aryl halides and aryl triflates was examined. The reaction with aryl iodides smoothly proceeded to afford the corresponding (1-fluorovinyl)arenes in the presence of a catalytic amount of CuI and Pd(PPh(3))(4) in aprotic polar solvents such as DMF, DMI, DMA, and NMP in good yields. A variety of functional groups (nitro, ester, ketone, and ether) on the aromatic rings can be tolerated under these mild conditions. Aryl iodides are superior to aryl bromides as the coupling reaction partner. The cross-coupling reaction of 1 with aryl triflates instead of aryl halides was also accomplished in the presence of tetrabutylammonium iodide (n-Bu(4)NI) as the additive under similar conditions.     

Direct aminoalkylation of arenes, heteroarenes, and alkenes via Ni-catalyzed Negishi cross-coupling reactions

A room-temperature Ni-catalyzed cross-coupling of aryl, heteroaryl, and alkenyl electrophiles with aminoalkylzinc bromides, readily available from the corresponding aminoalkyl chlorides via Grignard reagents, was developed. The reaction allows a convenient one-step preparation of various aminoalkyl products, including piperidine and tropane derivatives. Such functionalized amine moieties are widely present in various biologically active molecules. Aryl, heteroaryl, and alkenyl iodides, bromides, chlorides and triflates are suitable electrophiles. A short total synthesis of two natural products, (±)-galipinine and (±)-cusparine, is also reported.     

Scope of aminomethylations via Suzuki-Miyaura cross-coupling of organotrifluoroborates

We previously reported the Suzuki-Miyaura reaction of N,N-dialkylaminomethyltrifluoroborates with aryl bromides. Herein, we report a further investigation of the scope and limitations of this palladium-catalyzed aminomethylation reaction. Aryl chlorides, iodides, and triflates coupled in good to excellent yields to give N,N-dialkylbenzylic amines. The aminomethylation of alkenyl bromides was also examined.     

Suzuki-Miyaura cross-coupling reactions of potassium alkenyltrifluoroborates

We have previously reported that the palladium-catalyzed cross-coupling reaction of air-stable potassium alkenyltrifluoroborates with aryl halides and triflates proceeds readily with good yields. Recent progress in outlining the scope and limitations of such reactions is described herein. The palladium-catalyzed cross-coupling reaction of potassium alkenyltrifluoroborates with aryl and heteroaryl halides and triflates proceeds readily with moderate to excellent yields. The alkenyl cross-coupling reaction can generally be effected using 2 mol % of PdCl2(dppf).CH2Cl2 as catalyst in i-PrOH-H2O in the presence of t-BuNH2 as the base. A variety of functional groups are tolerated in both partners, and the process is stereospecific with regard to the alkenyltrifluoroborate starting material.     

Microwave-assisted amination from aryl triflates without base and catalyst

[reaction: see text] Aryl triflates are effectively converted to the corresponding anilines under microwave irradiation in 1-methyl-2-pyridone (NMP) without base and catalyst. Aryl triflates substituted with both electron-poor and electron-rich groups give good to excellent yields. It is noteworthy that the halogenated aryl triflates can chemoselectively react with amines to afford halogenated anilines.     

Palladium-catalyzed intermolecular coupling of aryl halides and amides

[formula: see text] The first general intermolecular C-N bond-forming reactions between aryl halides and amides were realized using a palladium catalyst with Xantphos as the ligand. Aryl triflates, carbamates, and sulfonamides are also viable substrates for the amidations, which proceed at 45-110 degrees C with 1-4 mol% of Pd catalyst in 66-99% yields and exhibit good functional group compatibility.     

Application of vinyl tris(trimethylsilyl)germanes in Pd-catalyzed couplings

The oxidative treatment of vinyltris(trimethylsilyl)germanes with hydrogen peroxide (NaOH/H(2)O/THF) or tert-butyl peroxide (KH/THF) generates reactive germanol or germanoxane species that undergo Pd-catalyzed cross-couplings with aryl and alkenyl halides and aryl triflates in the presence of Pd(PPh(3))(4). Vinylgermanes having either a conjugated or isolated double bond serve as versatile transmetalation reagents. The E-germanes undergo coupling with retention of stereochemistry under aqueous and anhydrous conditions, while coupling of Z-germanes occurs with less stereoselectivity to produce a mixture of E/Z products.     

Highly satisfactory alkynylation of alkenyl halides via Pd-catalyzed cross-coupling with alkynylzincs and its critical comparison with the sonogashira alkynylation

[reaction: see text] The Pd-catalyzed alkynylation of various alkenyl halides and triflates with alkynylzincs proceeds well even with alkynyl derivatives containing electron-withdrawing groups. The reaction appears to be highly general. Noteworthy is that the corresponding Sonogashira reactions under various reported conditions are significantly less satisfactory in all cases performed in this study.     

Intramolecular anti-hydrosilylation and silicon-assisted cross-coupling: highly regio- and stereoselective synthesis of trisubstituted homoallylic alcohols

A highly regio- and stereoselective anti-intramolecular hydrosilylation of alkynyl silyl ethers catalyzed by a ruthenium arene complex has been developed. The resultant (Z)-alkylidenesilacyclopentanes are efficiently coupled with aryl or alkenyl halides in the presence of tetrabutylammonium fluoride and a palladium(0) catalyst. The yields are generally good, and the reaction is compatible with a wide range of functional groups. The overall transformation achieves the stereoselective conversion of homopropargyl alcohols to trisubstituted homoallylic alcohols. [reaction: see text]     

Single‐Electron‐Transfer‐Induced Coupling of Arylzinc Reagents with Aryl and Alkenyl Halides

Arylzinc reagents, prepared from aryl halides/zinc powder or aryl Grignard reagents/zinc chloride, were found to undergo coupling with aryl and alkenyl halides without the aid of transition‐metal catalysis to give biaryls and styrene derivatives, respectively. In this context, we have already reported the corresponding reaction using aryl Grignard reagents instead of arylzinc reagents. Compared with the Grignard cross‐coupling, the present reaction features high functional‐group tolerance, whereby electrophilic groups such as alkoxycarbonyl and cyano groups are compatible as substituents on both the arylzinc reagents and the aryl halides. Aryl halides receive a single electron and thereby become activated as the corresponding anion radicals, which react with arylzinc reagents, thus leading to the cross‐coupling products.     

Stereo-recognizing transformation of (E)-alkenyl halides into sulfides catalyzed by nickel(0) triethyl phosphite complex

(E)-Alkenyl halides were transformed into (E)-alkenyl sulfides by the nickel(0) triethyl phosphite complex-catalyzed reaction with thiols, whereas (Z)-alkenyl halides gave alkynes under the same reaction conditions. Aryl halides were also transformed into aryl sulfides using the same reagent system.     

Iron‐Catalyzed Cross‐Coupling of Alkenyl Acetates

Stable C O linkages are generally unreactive in cross‐coupling reactions which mostly employ more electrophilic halides or activated esters (triflates, tosylates). Acetates are cheap and easily accessible electrophiles but have not been used in cross‐couplings because the strong C O bond and high propensity to engage in unwanted acetylation and deprotonation. Reported herein is a selective iron‐catalyzed cross‐coupling of diverse alkenyl acetates, and it operates under mild reaction conditions (0 °C, 2 h) with a ligand‐free catalyst (1–2 mol %).     

Stereocontrolled synthesis of bicyclic ureas and sulfamides via Pd-catalyzed alkene carboamination reactions

The synthesis of bicyclic ureas and sulfamides via palladium-catalyzed alkene carboamination reactions between aryl/alkenyl halides/triflates and alkenes bearing pendant cyclic sulfamides and ureas is described. The substrates for these reactions are generated in 3–5 steps from commercially available materials, and products are obtained in good yield with up to >20:1 diastereoselectivity. The stereochemical outcome of the sulfamide alkene addition is consistent with a mechanism involving anti-aminopalladation of the alkene, whereas the stereochemical outcome of the urea alkene addition is consistent with a syn-aminopalladation mechanism.     

Direct synthesis of primary arylamines via C-N cross-coupling of aryl bromides and triflates with amides

Aryl halides and triflates are coupled with primary amides to give the corresponding arylamines in the presence of a palladium catalyst, a suitable ligand, and a base. The catalyst system performs well for a large number of different substrates at 100-150 °C without solvent, and with low catalyst levels (0.12 mol % Pd). Nicotinamide might be useful as a nitrogen source in the Pd-catalyzed amination reaction.     

An efficient Negishi cross-coupling reaction catalyzed by nickel(II) and diethyl phosphite

A combination of diethyl phosphite-DMAP and Ni(II) salts forms a very effective catalytic system for the cross-coupling reactions of arylzinc halides with aryl, heteroaryl, and alkenyl bromides, chlorides, triflates, and nonaflates. The choice of solvent is quite important and the mixture of THF-N-ethylpyrrolidinone (NEP) (8:1) was found to be optimal. The reaction usually requires only 0.05 mol % of NiCl₂ or Ni(acac)₂ as catalyst and proceeds at room temperature within 1-48 h.     

Application of silicon-based cross-coupling technology to triflates

Aryl silatranes undergo fluoride-induced cross-coupling with aryl triflates to provide unsymmetrical biaryl derivatives in good to excellent yields. Silatranes also couple with aryl iodides and bromides, although the yields of adduct are lower than with the corresponding siloxane derivates. Aryl siloxanes (which had previously failed to couple with triflates) can be employed for triflate couplings using the Denmark modification, although the yields are lower than the corresponding silatrane reactions.     

Aryl transfer between Pd(II) centers or Pd(IV) intermediates in Pd-catalyzed domino reactions

A computational study has been performed to determine the mechanism of the key steps of Pd-catalyzed domino reactions in which C(sp2)-C(sp2) are formed from aryl and alkenyl halides. DFT calculations were done on model complexes of the proposed intermediates, with PH3 and H2O as ancillary ligands, to explore two possible mechanisms: the oxidative addition of aryl or alkenyl halides to palladacycles to give Pd(IV) intermediates, and the transmetalation-type reaction of aryl or alkenyl ligands between two Pd(II) centers, a palladacycle, and a Pd(II) complex formed by oxidative addition of aryl or alkenyl halides to Pd0. We have shown that oxidative addition of iodoethylene to Pd0 precursors is more favorable than oxidative addition to Pd(II) palladacycles, whereas transmetalation-type reactions between Pd(II) complexes are facile. Similar results were obtained with iodobenzene instead of iodoethylene and formamide as the ancillary ligand. These results suggest that Pd(IV) intermediates are not involved in these reactions.     

Phase-transfer catalysis in the nickel- and palladium-catalyzed formation of aryl and alkenyl sulfides

Aryl and alkenyl sulfides can be conveniently prepared from the corresponding halides and alkaline thiolates under phase transfer conditions in the presence of σ-Aryl-Ni[P(C₆H₅)₃]₂Cl or σ-Aryl-Pd[P(C₆H₅)₃]₂Br.