Palladium-catalyzed cross-coupling reaction of alkenyl bromides with potassium alkyltrifluoroborates

The Suzuki-Miyaura-type cross-coupling reaction of potassium alkyltrifluoroborates with various alkenyl bromides in the presence of 10 mol % of PdCl₂(dppf)·CH₂Cl₂ and 3.0 equiv of Cs₂CO₃ in aqueous toluene at 80 °C provided the desired compounds in 63-95% yields. A variety of functional groups in the potassium alkyltrifluoroborates were tolerated under the basic conditions.     

Ruphos-mediated Suzuki cross-coupling of secondary alkyl trifluoroborates

A Ruphos-mediated Suzuki cross-coupling between (hetero)aryl bromides and secondary alkyltrifluoroborates is described using palladium catalysis. The Ruphos ligand showed superior properties as compared to S-Phos in this type of reaction. This method constitutes a valuable extension to current methods for the straightforward production of secondary-alkylated (hetero)aryl derivatives.     

Photoinduced reaction of potassium alkyltrifluoroborates,sulfur dioxide and para-quinone methides via radical 1,6-addition

A photoinduced reaction of potassium alkyltrifluoroborates, sulfur dioxide, and para-quinone methides under visible light irradiation at room temperature is developed, giving rise to diarylmethyl alkylsulfones in moderate to good yields. This reaction works well under photocatalysis with a broad substrate scope by using DABCO·(SO₂)₂ as the source of sulfur dioxide. Mechanistic study shows that this transformation is initiated by alkyl radicals generated in situ from potassium alkyltrifluoroborates in the presence of photocatalyst. The subsequent insertion of sulfur dioxide and radical 1,6-addition of para-quinone methides with alkylsulfonyl radical intermediates afford the corresponding diarylmethyl alkylsulfones.     

Immobilization of copper in organic-inorganic hybrid materials: a highly efficient and reusable catalyst for the Ullmann diaryl etherification

The immobilization of copper in organic-inorganic hybrid materials catalyzing the Ullmann reaction has been described. Phenols reacted with aryl iodides, aryl bromides and aryl chlorides smoothly in the presence of a 3-(2-aminoethylamino)propyl functionalized silica gel immobilized copper catalyst. The protocol involved the use of DMSO as the solvent, and potassium fluoride as the base. The reactions generated the corresponding cross-coupling products in good to excellent yields. Furthermore, the silica-supported copper could be recovered and recycled by a simple filtration of the reaction solution and used for 10 consecutive trials without loss of its reactivity.     

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.     

Development of the suzuki-miyaura cross-coupling reaction: use of air-stable potassium alkynyltrifluoroborates in aryl alkynylations

The palladium-catalyzed cross-coupling reaction of potassium alkynyltrifluoroborates with aryl halides or triflates proceeds readily with moderate to excellent yields. The potassium alkynyltrifluoroborates are air- and moisture-stable crystalline solids that can be stored indefinitely, which will provide an advantage in applications to combinatorial chemistry. The alkynyl cross-coupling reaction can be effected using 9 mol % of PdCl2(dppf).CH2Cl2 as catalyst in THF or THF-H2O in the presence of Cs2CO3 as the inorganic base. A variety of functional groups are tolerated in both partners.     

Stereoselective synthesis of 2-alkenylaziridines and 2-alkenylazetidines by palladium-catalyzed intramolecular amination of alpha- and beta-amino allenes.

Whereas palladium-catalyzed reaction of N-arylsulfonyl-alpha-amino allenes with an aryl iodide (4 equiv) in the presence of potassium carbonate (4 equiv) in DMF at around 70 degrees C affords the corresponding 3-pyrroline derivatives, the reaction in refluxing 1,4-dioxane under otherwise identical conditions yields exclusively or most predominantly the corresponding 2-alkenylaziridines bearing an aryl group on the double bond. Similarly, N-arylsulfonyl-beta-amino allenes can be also cyclized into the corresponding alkenylazetidines bearing a 2,4-cis-configuration under palladium-catalyzed cyclization conditions in DMF.     

The influence of the nature of phosphine ligand on palladium catalysts for cross-coupling of weakly nucleophilic potassium pentafluorophenyltrifluoroborate with ArHal and PhCH2Hal (Hal=Br,Cl)

The influence of the ligand nature on catalytic activity of palladium catalysts for cross-coupling of weakly nucleophilic potassium pentafluorophenyltrifluoroborate, which imitates the behavior of electron-deficient organoboron reagents, with aryl halides, ArHal (Hal=Br, Cl) was studied. The activity of the catalysts generated in situ from Pd(OAc)₂ and appropriate phosphorous containing ligands and the reaction selectivity was found to depend on the nature of bulky phosphines used as ligands. As a result, conditions for involving the electron-deficient organoboron reagent—potassium pentafluorophenyltrifluoroborate—in the palladium-catalyzed cross-coupling with aryl bromides and aryl chlorides were identified. It was demonstrated that the chosen conditions are appropriate for the reaction of K[C₆F₅BF₃] with benzyl chloride and benzyl bromide deriving pentafluorophenylarylmethanes, C₆F₅CH₂Ar.     

Plant coumarins: XI. Cross coupling reactions with 2-(tosyl)oreoselone

The reaction of a linearly fused furocoumarin, oreoselone, with p-toluenesulfonyl chloride gave 2-tosyloreoselone which showed a high reactivity in palladium-catalyzed cross-coupling reactions with formation of a new carbon-carbon bond. 2-Tosyloreoselone reacted with terminal alkynes in the presence of Pd(PPh₃)₂Cl₂ to give the corresponding 2-alkynylfuro[3,2-g]chromen-3-ones. 2-Aryl(hetaryl)alkynyloreoselones were obtained in high yield directly by palladium-catalyzed reaction of oreoselone with tosyl chloride and aryl(hetaryl)acetylenes. The reaction of 2-tosyloreoselone with aryl(hetaryl)boronic acids in the presence of palladium complexes with uni- and bidentate ligands, tetrabutylammonium bromide, and a base afforded 2-aryl(hetaryl)-substituted oreoselones. 2-Vinyloreoselone was synthesized from 2-tosyloreoselone and potassium trifluoro(vinyl)borate.     

A New Route to N‐Aryl 2‐Alkenamides,N‐Allyl N‐Aryl 2‐Alkenamides,and N‐Aryl α,β‐Unsaturated γ‐Lactams from N‐Aryl 3‐(Phenylsulfonyl)propanamides

A series of N‐aryl 2‐alkenamides were produced efficiently by treating N‐aryl 3‐(phenylsulfonyl)‐propanamides with potassium tert‐butoxide in THF at 0°C. With out isolation, it was further treated with an additional equivalent of potassium tert‐butoxide and allyl bromide to give N‐allyl N‐aryl 2‐alkenamides in one pot in good yields. Followed by a ring‐closing metathesis reaction, these N‐allyl N‐aryl 2‐alkenamides were respectively converted into corresponding N‐aryl α,β‐unsaturated γ‐lactams in moderate yields.     

Suzuki-Miyaura cross-coupling reactions of potassium vinyltrifluoroborate with aryl and heteroaryl electrophiles

We have previously reported that the palladium-catalyzed cross-coupling reaction of potassium vinyltrifluoroborate with aryl electrophiles proceeds with good yields. Herein, we describe recent progress in optimizing the reaction, as well as outlining the scope and limitations of the reaction. The cross-coupling reaction can generally be effected using 2 mol % of PdCl2 and 6 mol % of PPh3 as a catalyst system in THF/H2O with Cs2CO3 as a base. Moderate to good yields are obtained in the presence of a variety of functional groups.     

Palladium-Catalyzed Synthesis of 1,3-Dienes from Allenes and Organic Halides

A wide range of aryl and vinylic halides react with 1,1-dimethylallene (2a) and potassium carbonate in the presence of Pd(dba)(2) (dba = dibenzylideneacetone) in N,N-dimethylacetamide (DMA) at temperature 100-120 degrees C to give the corresponding dienes CH(2)C(CH(3))CRCH(2) (3a-o), where R is aryl or vinylic, in good to excellent yields. Higher yields of diene products were obtained for aryl bromides than for the corresponding aryl iodides and chlorides. Under similar reaction conditions, tetramethylallene (2b), 1-methyl-1-phenylallene (2c), 1-methyl-3-phenylallene (2d), and 1-cyclohexylallene (2e) also react with aryl and vinylic halides to give diene products (3p-w). For 2d, both E and Z isomers 3t and 3u of the diene product were observed. For 2e, two regioisomers 3vand 3w were isolated with 3w likely from alkene isomerization of 3v. Various palladium systems were tested for the catalytic activity of diene formation. In addition to Pd(dba)(2)/PPh(3), Pd(OAc)(2)/PPh(3), PdCl(2)(PPh(3))(2), and PdCl(2)(dppe) are also very effective as catalysts for the reaction of 2a with p-bromoacetophenone (1a) to give 3a. Studies on the effect of solvents and bases show that DMA and K(2)CO(3) are the solvent and base that give the highest yield of diene 3a. Possible mechanisms for this catalytic diene formation are proposed.     

General and efficient methodology for the Suzuki-Miyaura reaction in technical grade 2-propanol

The reaction profile of a series of palladium-based catalysts was examined in the Suzuki-Miyaura reaction using technical grade 2-propanol as solvent and potassium t-butoxide as base. The results generally show high activity. The method allows for the coupling of electron-rich aryl chlorides with sterically hindered aryl boronic acids to produce tri-ortho-substituted biaryls in high yields using very mild conditions and short reaction times.     

Synthesis of c-17 trans β-lactams of the androstane series

3,3′-Ethylenedioxyandrost-4-en-17β-ol 1 was converted into the ethyl ester 2 by reaction with potassium metal and ethyl chloroacetate. The ethyl ester 2 on reaction with hydrazine gave the hydrazide 3 . Condensation of 3 with aryl aldehydes gave the Schiff bases 4 . The reaction of Schiff bases 4 with mono-chloroacetyl chloride in the presence of triethylamine afforded the β-lactams 5 .     

Palladium-catalyzed Suzuki–Miyaura cross-coupling reaction of potassium 2-pyridyl trifluoroborate with aryl (heteroaryl) halides

Palladium-catalyzed Suzuki–Miyaura cross-coupling reaction of potassium pyridine-2-trifluoroborates and various aryl (heteroaryl) halides can generate the corresponding desired coupling products with moderate to good yields. It can be carried out under the conditions with ethanol as solvent, Pd(OAc)₂ and SPhos as catalyst system and Na₂CO₃ as a base.     

Nickel(II) complex containing N‐(4,5‐dihydrooxazol‐2‐yl)benzamide ligands: highly efficient catalyst for Heck coupling reactions

Heck reaction catalyzed by Ni(II) containing N‐(4,5‐dihydrooxazol‐2‐yl) benzamide has been developed. The coupling of alkenes with aryl iodide or aryl bromide in the presence of potassium carbonate in DMF provides the corresponding products with moderate to good yields. This method possesses obvious advantages such as low‐cost catalyst and simple experimental operation. Copyright © 2014 John Wiley & Sons, Ltd.     

Weakly nucleophilic conjugate bases of superacids as powerful nucleophiles in vinylic bimolecular nucleophilic substitutions of simple β-alkylvinyl(aryl)-λ3-bromanes

We report herein, for the first time, the stereoselective synthesis of simple (E)-β-alkylvinyl(aryl)-λ(3)-bromanes via a boron-λ(3)-bromane exchange reaction and their unique bimolecular nucleophilic substitutions at the vinylic ipso carbon atom under mild conditions. Interestingly, even weakly nucleophilic anions such as conjugate bases of superacids (HBF(4), TfOH, Tf(2)CH(2), Tf(3)CH, Tf(2)NH, etc.) function as nucleophiles toward the vinyl-λ(3)-bromanes. For instance, the vinylic S(N)2 reaction of (E)-vinyl-λ(3)-bromanes with potassium bis(triflyl)methanide stereoselectively produced (Z)-vinyloxy oxosulfonium ylides with exclusive inversion of configuration via oxygen attack, while that with potassium bis(triflyl)imide afforded predominantly (Z)-vinyloxysulfoximines. In marked contrast, (E)-β-alkylvinyl-λ(3)-iodanes do not undergo the vinylic S(N)2 reaction with these conjugate bases of superacids. The differences between the nucleofugalities of aryl-λ(3)-iodanyl and aryl-λ(3)-bromanyl groups (the latter being greater) probably play a pivotal role in these unique reactions.     

One-pot synthesis of symmetrical and unsymmetrical aryl sulfides by Pd-catalyzed couplings of aryl halides and thioacetates

Aryl sulfides were obtained from the coupling reaction of S-aryl (or S-alkyl) thioacetates and aryl bromides in the presence of palladium catalyst. This reaction method enables the one-pot synthesis of symmetrical and unsymmetrical diaryl sulfides by employing potassium thioacetate with aryl iodides and aryl bromides.     

Synthesis of 1-aryl-substituted-4-chloroimidazo[1,2-a]quinoxalines catalyzed by PdCl2 in water

The reaction of 2-chloro-3-propargylaminoquinoxaline with various aryl iodides and bromides catalyzed by Pd–Cu in the presence of potassium carbonate as the base in water leads to the one-pot formation of 1-aryl-substituted-4-chloroimidazo[1,2-a]quinoxalines in moderate-to-high yields.     

Synthesis and Reactions of 3‐Methylthiazolo[3,2‐a]Benzimidazole‐2‐Carboxylic Acid Hydrazide: Synthesis of Some New Pyrazole, 1,3‐Thiazoline, 1,2,4‐Triazole and 1,2,4‐Triazolo[3,4‐b]‐1,3,4‐Thiadiazine Derivatives Pendant to Thiazolo[3,2‐a]Benzimidazole Moiety

The reaction of 3‐methylthiazolo[3,2‐a]benzimidazole‐2‐carboxylic acid ethyl ester (1) with hydrazine hydrate gives the hydrazide 2 which reacts with CS₂/KOH to afford the potassium salt 3. Treatment of 3 with l‐aryl‐2‐bromoethanones 4a,b afforded the 1,3‐thiazoline derivatives 6a,b, respectively, while the reaction of 3 with hydrazine hydrate afforded 1,2,4‐triazole‐3‐thione derivative 9. The reaction of 9 with l‐aryl‐2‐bromoethanones 4a,b and with hydrazonyl chlorides 11a,b gave the 1,2,4‐triazolo[3,4‐b]‐1,3,4‐thiadiazine derivatives 10a,b and 12a,b, respectively. Treatment of hydrazide 2 with phenyl isothiocyanate in refluxing benzene gave the thiosemicarbazide derivative 16. The latter reaction gave 1,3,4‐oxadiazole derivative 17 when benzene was replaced by DMF. Cyclization of the thiosemicarbazide derivative 16 with NaOH resulted in the formation of the 1,2,4‐triazole‐3‐thione derivative 18.