N-Phenacylpyridinium bromides in the one-pot synthesis of 2,3-dihydrofurans

A one-pot three-component process for the synthesis of highly functionalized 2,3-dihydrofurans from 1,3-dicarbonyl compounds, aromatic aldehydes, and N-phenacylpyridinium bromides has been developed. Benzylidene 1,3-dicarbonyl compounds could be generated in situ from aromatic aldehydes and 1,3-dicarbonyl compounds and then reacted smoothly with N-phenacylpyridinium bromides to produce 2,3-dihydrofurans in moderate to good yields. Piperidine/acetonitrile is the optimal condition for this process. To increase the efficiency of this reaction, this one-pot process was also conducted solvent-free under classical heating conditions and grinding conditions.     

Convenient synthesis of 1a,1b,2,5-tetrahydro-1H-5a-aza-cyclopropa[a]indenes by base promoted cyclodimerization of 1,1-dicyano-2-aryl-3-benzoylcyclopropanes

1,1-Dicyano-2-aryl-3-benzoylcyclopropanes in acetonitrile in the presence of triethylamine underwent cyclodimerization reaction to afford the novel polyfunctionalized 1a,1b,2,5-tetrahydro-1H-5a-aza-cyclopropa[a]indenes in moderate yields. These polycyclic compounds can be more conveniently synthesized by the one-pot domino reaction of N-phenacylpyridinium bromides with arylidene malononitriles.     

Mild and efficient methods for the conversion of benzylic bromides to benzylic thiols

Very mild and efficient methods are established for the conversion of the benzylic bromides at room temperature to their corresponding benzylic thiols with high yields (94-99%) in 1 h under N₂.     

Oxidation of disulfides with electrophilic halogenating reagents: concise methods for preparation of thiosulfonates and sulfonyl halides

The reaction of aromatic or benzylic disulfides with 2.5 equiv of Selectfluor™ in acetonitrile/water (10:1) at room temperature efficiently produced the corresponding thiosulfonates. Conversely, the reaction of disulfides with 6.5 equiv of Selectfluor™ or thiosulfonates with 4.5 equiv of Selectfluor™ in refluxing acetonitrile/water (10:1) provided sulfonyl fluorides in high yields. Accufluor™ and FP-T300™ are also effective in preparing sulfonyl fluorides from disulfides under the similar reaction conditions. Sulfonyl chlorides or sulfonyl bromides were effectively obtained from the reaction of disulfides with 6 equiv of either N-chlorosuccinimide or N-bromosuccinimide in acetonitrile/water (10:1) at room temperature. Some other electrophilic chlorinating or brominating reagents are also able to be used instead of N-chlorosuccinimide or N-bromosuccinimide for the syntheses of sulfonyl halides from disulfides. These reactions of disulfides with electrophilic halogenating reagents are convenient methods to prepare thiosulfonates and sulfonyl halides.     

Indium- and zinc-mediated Barbier-type allylations of an N,N-(dimethylsulfamoyl)-protected aldimine and subsequent deprotection

Barbier-type Zn and In-mediated allylations of an N,N-(dimethylsulfamoyl)-protected aldimine with different allyl bromides were investigated for the preparation of N-homoallylic sulfamides. The desired N,N-(dimethylsulfamoyl)-protected products were obtained in moderate to high yields in THF as the optimal solvent. Their further derivatization was demonstrated by a facile preparation of a functionalized dehydropiperidine by an allylation/olefin metathesis reaction sequence. A high yielding deprotection of the N,N-dimethylsulfamoyl group was likewise demonstrated.     

Intramolecular dehydrochlorination of [2-(N’,N’-dialkylhydrazino)ethyl]phosphonium salts. Chemoselective alkaline hydrolysis of triphenylphosphonioalkylhydrazinium salts

The reactions of N,N-dimethylhydrazine and N-aminopiperidine with potential triphenylvinyl-and-propenylphosphonium bromides were used to obtain adducts by the α,β-double bonds of the latter. The resulting [2-(N’,N’-dimethylhydrazino)ethyl]phosphonium salts just on moderate heating in alcohol undergo dehydration leading to the corresponding hydrazone or α,β-unsaturated hydrazine derivatives. Contrary to that, [2-(N’,N’dimethylhydrazino)-2-methylethyl]triphenylphosphonium bromide under the same conditions does not undergo dehydration. The reaction of (3-bromopropyl)-and (4-bromobutyl)triphenylphosphonium bromides with N,N-dimethylhydrazine gives phosphoniohydrazinium salts with a tri-or tetramethylene common radical. When treated with equimolar amount of ethanolic sodium ethylate, the latter products undergo alkaline reduction of one of the phenyl groups to give the corresponding diphenylphosphinoylalkylhydrazinium salts in high yields.     

Heck cross-coupling of vinyl heteroaromatic compounds with aryl and heteroaryl halides using Pd(II) complex under phosphine-free conditions

The palladium-catalyzed cross-coupling reaction of vinyl heteroaromatic compounds with aryl bromides and heteroaryl bromides is described using air and moisture stable N,N′,N″,O-tetrafunctional Pd catalyst under phosphine-free conditions. As a result a variety of trans-1,2-disubstituted vinyl heterocycles were obtained in high to good yields.     

Copper(I) 3-methylsalicylate,an efficient catalyst for N-arylation of heterocycles under moderate reaction conditions

Copper(I) 3-methylsalicylate mediates N-arylation reactions of both aliphatic and aromatic heterocycles under moderate reaction conditions. Both electron rich and electron poor aryl bromides and a diverse set of N-heterocycles were allowed to react and gave N-arylation products in high yields which demonstrated the efficiency and utility of this catalyst.     

Air-oxidized products of multi-component reactions between 3-amino-1,2,4-triazole, aromatic aldehydes and isonitriles

The Groebke-type multi-component reaction (MCR) between 3-amino-1,2,4-triazole, aromatic aldehydes and isonitriles has been studied from the viewpoint of convenient generation of combinatorial arrays of imidazo[1,2-b][1,2,4]triazoles. However, it was established that the desired heterocyclic structures can be produced in moderate to good yields in an oxidized form, when benzylic isonitriles are used. Oxidation occurred at the benzylic position to produce N-alkylidene-4H-imidazo[1,2-b][1,2,4]triazol-6-amines that proved to be unusually stable towards acid hydrolysis and reduction. The presence of an easily oxidized benzylic position in the target structures is thought to be the prerequisite for successful Groebke-type MCR of 3-amino-1,2,4-triazole.     

Indium-mediated cleavage of diphenyl diselenide and diphenyl disulfide: efficient one-pot synthesis of unsymmetrical diorganyl selenides, sulfides, and selenoesters

A convenient and efficient method was developed for the synthesis of alkyl phenyl selenides, sulfides, and selenoesters in one-pot reaction by using indium metal. The reaction showed the selectivity for tert-alkyl, benzylic, and allylic halides over primary and secondary alkyl halides. For the reaction of primary and secondary alkyl iodides and bromides, the yields of selenides were improved by the addition of a catalytic amount of iodine.     

Benzylic C-H activation and C-O bond formation via aryl to benzylic 1,4-palladium migrations

A procedure for benzylic C-H activation has been developed using a palladium 1,4-aryl to benzylic migration as a key step. Carboxylates and phenoxides readily trap the resulting benzylic palladium intermediates obtained from palladium ‘through space’ migration. Aryl bromides and iodides have been successfully employed in this reaction, furnishing moderate to good yields. The mechanism of this reaction has been studied by deuterium-labeling experiments, which suggest that the migration of palladium from an aryl to a benzylic position occurs reversibly. The reaction conditions developed for the migration process also oxidize the neighboring benzylic alcohols to the corresponding aldehydes and ketones.     

Palladium-catalyzed cascade one-pot synthesis of 5-arylmethylisoxazolidines from N-homoallylhydroxylamines with aryl bromides

A novel method for the synthesis of 5-arylmethylisoxazolidines via palladium-catalyzed reactions of aryl bromides with N-homoallylhydroxylamines is described. This reaction effects intramolecular C-O bond formation with concomitant intermolecular formation of a C-C bond in moderate to good yields. Moderate to excellent diastereoselectivities are observed for the formation of the isoxazolidines. The catalytic system has a tolerance to a wide variety of functional groups.     

Practical one-pot conversion of aryl bromides and β-bromostyrenes into aromatic nitriles and cinnamonitriles

Various aryl bromides were efficiently converted into the corresponding aromatic nitriles in good yields by the treatment with Mg turnings and subsequently DMF, followed by treatment with molecular iodine and aq NH₃. The same treatment of aryl bromides, which are weakly reactive to Mg turnings, with ⁱPrMgCl·LiCl and subsequently DMF, followed by the treatment with molecular iodine and aq NH₃ also afforded the corresponding aromatic nitriles in good yields. On the other hand, when N-formylpiperidine was used instead of DMF, p-substituted β-bromostyrenes were converted into the corresponding p-substituted cinnamonitriles, i.e., α,β-unsaturated nitriles, in good to moderate yields by the same procedure. The reactions were carried out by means of a simple experimental procedure and did not require any toxic metal cyanides or expensive rare metals. Therefore, the present reactions are practical and environmentally benign one-pot methods for the preparation of aromatic nitriles, cinnamonitriles, and aliphatic nitriles from aryl bromides, β-bromostyrenes, and alkyl bromides, respectively, through the formation of Grignard reagents and their DMF or N-formylpiperidine adducts.     

Gold(I)-catalyzed direct C-H arylation of pyrazine and pyridine with aryl bromides

An efficient procedure for the direct C-H arylation of electron-poor aromatics such as pyrazine and pyridine with aryl bomides is described. In the presence of catalytic amount of Cy₃PAuCl and with the use of t-BuOK as base, pyrazine undergoes the direct C-H arylation with aryl bromides at 100 °C, and the yields of the arylated products depend on the nature of aryl bromides. In the cases of electron-rich aryl bromides used, the arylated pyrazines can be obtained in good to high yields. For electron-poor aryl bromides, the addition of AgBF₄ is the crucial point to accelerate the coupling reaction to give the arylated products in moderate yields. Pyridine also reacts with electron-rich aryl bromides catalyzed by Cy₃PAuCl to give a mixture of arylated regioisomers in moderate yield. However, in order to realize the direct C-H arylation of pyridine with electron-poor aryl bromides, the addition of silver salt as additive and a milder reaction temperature (60 °C) are required.     

Benzylic bromination catalyzed by triphenylphosphine selenide via Lewis basic activation

The synthesis of benzyl bromides was achieved under mild reaction conditions using N-bromosuccinimide as a bromine source and triphenylphosphine selenide as a catalyst. These conditions were compatible with a variety of substrates including boronic esters, protected amines to give imines, and carboxylic acids (to give phthalides when ortho to the benzylic center). A preliminary mechanistic investigation utilizing calculated bond dissociation energies (BDE) is employed to rationalize how a Lewis base can activate a radical mechanism.     

Palladium-catalyzed Heck reaction of in-situ generated benzylic iodides and styrenes

A palladium-catalyzed Heck reaction of in-situ generated benzylic iodides and styrenes has been achieved. The reaction proceeds in a one-pot manner through 1) addition perfluoroalkyl iodides to styrenes to give benzylic iodides, 2) followed by a palladium-catalyzed Heck coupling of the resulting benzylic iodides with the same alkenes in high regio- and stereoselectivity. A variety of perfluoroalkylated alkenes were obtained in moderate to excellent yields.     

Palladium-catalyzed benzylic C(sp3)–H carbonylative arylation of azaarylmethyl amines with aryl bromides

A highly selective palladium-catalyzed carbonylative arylation of weakly acidic benzylic C(sp³)–H bonds of azaarylmethylamines with aryl bromides under 1 atm of CO gas has been achieved. This work represents the first examples of use of such weakly acidic pronucleophiles in this class of transformations. In the presence of a NIXANTPHOS-based palladium catalyst, this one-pot cascade process allows a range of azaarylmethylamines containing pyridyl, quinolinyl and pyrimidyl moieties and acyclic and cyclic amines to undergo efficient reactions with aryl bromides and CO to provide α-amino aryl-azaarylmethyl ketones in moderate to high yields with a broad substrate scope and good tolerance of functional groups. This reaction proceeds via in situ reversible deprotonation of the benzylic C–H bonds to give the active carbanions, thereby avoiding prefunctionalized organometallic reagents and generation of additional waste. Importantly, the operational simplicity, scalability and diversity of the products highlight the potential applicability of this protocol.

Introduced is a method for the deprotonative carbonylation of azaarylmethyl amines with aryl bromides. The reaction employs a Pd(NIXANTPHOS)-based catalyst and takes place under 1 atm CO.     

Catalytic CN Bond Alkynylation of N‐Benzylic Sulfonamides with Terminal Alkynes

A new cross‐coupling reaction of N‐benzylic sulfonamides with terminal alkynes for the synthesis of internal alkynes is reported. In the presence of 5 mol% of (Tf)₂NH/Bi(OTf)₃ (1:1), a broad range of N‐benzylic sulfonamides react smoothly with arylacetylenes to afford structurally diverse internal alkynes in moderate to excellent yields. We reasoned that vinyl cations could be formed by the regioselective attack of terminal alkynes with benzyl cations generated in situ from N‐benzylic sulfonamides under acidic conditions, which then eliminated to form a carbon‐carbon triple bond.     

A new method for the synthesis of dithiocarbamates by CuI-catalyzed coupling reaction

The Ullmann-type coupling reaction of sodium dithiocarbamates with aryl iodides and vinyl bromides catalyzed by CuI/N,N-dimethylglycine proceeds smoothly in DMF at 110 °C to give corresponding dithiocarbamates in good yields.     

Palladium-catalysed direct arylations of NH-free pyrrole and N-tosylpyrrole with aryl bromides

The palladium-catalysed direct coupling of aryl halides with pyrroles provides a greener access to arylated pyrroles than more classical couplings such as Suzuki, Stille or Negishi reactions. However, so far, NH-free pyrrole and N-tosylpyrrole gave disappointing results for such couplings either in terms of regioselectivity of the arylation, catalyst loading or substrate scope. The reactivity of both NH-free pyrrole and N-tosylpyrrole was studied, and the tosylated pyrrole led to higher yields of coupling products due to better conversions of the aryl bromides. A range of aryl bromides undergo regioselective coupling at C2 of N-tosylpyrrole in moderate to good yields using 1 mol % [Pd(Cl(C₃H₅)]₂ as the catalyst, KOAc as the base in DMAc.