Efficient and regioselective 9-endo cyclization of α-carbamoyl radicals

With the promotion of Lewis acid BF(3)?OEt(2), various N-(hex-5-enyl)-2-iodoalkanamides underwent efficient and regioselective 9-endo iodine-atom-transfer radical cyclization reactions at room temperature. The cyclized products were readily converted to the corresponding azonan-2-ones by reduction with Bu(3)SnH or to hexahydroindolizin-3(5H)-ones by treatment with aqueous Na(2)CO(3) in a one-pot, two-stage manner.     

Highly regioselective lipase-catalyzed acetylation and hydrolysis of acyclic α,ω-terpenediols and their diacetates

Highly regioselective transformations of the acyclic α,ω-terpenediols and their diacetates to the monoacetates using lipase were accomplished. The acetylation of the α,ω-terpenediols gave regioselectively the ω-monoacetates 3, whereas the α-monoacetates 2 were obtained by hydrolysis of the α,ω-diacetates.     

Convenient synthesis of α-diarylmethylphosphonates by HOTf catalyzed Friedel-Crafts arylation of α-aryl α-hydroxyphosphonates

We report a convenient catalytic Friedel-Crafts arylation of α-aryl α-hydroxyphosphonates with various (hetero)aromatic compounds. HOTf (trifluoromethanesulfonic acid) is identified to be the best Brønsted acid catalyst, and the desired α-diarylmethylphosphonates were obtained in up to 41–95% yield.     

Claisen rearrangement of allylic α-isocyano-esters—regioselective allylation of α-isocyanoesters at the α-carbon

A regioselective allylation of α-isocyanoesters at the α-carbon was achieved by the Claisen rearrangement of allylic α-isocyanoesters via the corresponding silyl ketene acetals in situ generated.     

Synthesis of indenoindene-fused α-methylene-γ-butyrolactones via a tandem intra- and intermolecular Friedel-Crafts reaction

An efficient synthesis of indenoindene-fused α-methylene-γ-butyrolactones was carried out via a tandem intra- and intermolecular Friedel-Crafts reaction from the spiro-lactone, which can be easily prepared from ninhydrin by indium-mediated Barbier reaction of cinnamyl bromide.     

Metal-free and highly regioselective synthesis of N-heteroaryl substituted pyrazoles from α,β-unsaturated N-tosylhydrazones and heteroaryl chlorides

A cascade cyclization/nucleophilic aromatic substitution (S_NAr) reaction of α,β-unsaturated N-tosylhydrazones with N-heteroaryl chlorides was developed for the synthesis of N-heteroaryl pyrazole derivatives. This one-pot reaction provided bi(heteroaryl) derivatives in good to excellent yields and with excellent regioselectivity. The procedure is operationally simple and applicable to large-scale synthesis.     

Iron-catalyzed, highly regioselective synthesis of α-aryl carboxylic acids from styrene derivatives and CO2

The iron-catalyzed hydrocarboxylation of aryl alkenes has been developed using a highly active bench-stable iron(II) precatalyst to give α-aryl carboxylic acids in excellent yields and with near-perfect regioselectivity. Using just 1 mol % FeCl(2), bis(imino)pyridine 6 (1 mol %), CO(2) (atmospheric pressure), and a hydride source (EtMgBr, 1.2 equiv), a range of sterically and electronically differentiated aryl alkenes were transformed to the corresponding α-aryl carboxylic acids (up to 96% isolated yield). The catalyst was found to be equally active with a loading of 0.1 mol %. Preliminary mechanistic investigations show that an iron-catalyzed hydrometalation is followed by transmetalation and reaction with the electrophile (CO(2)).     

Facile synthesis of 2-pyrazolines and α,β-diamino ketones via regioselective ring-opening of hydrazone-tethered aziridines

A facile strategy to access 2-pyrazolines and α,β-diamino ketones via SN(2)-type ring-opening of N-(aziridin-2-ylethylidene)hydrazines or N-(aziridin-2-ylbutylidene)hydrazines in the presence of Lewis acid or trifluoromethanesulfonic acid (TfOH) is described in this context.     

Copper-catalyzed highly regioselective silylcupration of terminal alkynes to form α-vinylsilanes

A highly regioselective synthesis of branched vinylsilanes through silicon-copper additions to terminal alkynes catalyzed by copper(I) was developed using methanol as additive. The corresponding vinylsilanes were obtained with excellent branched to linear selectivity of up to 99/1 in good yields.     

Note Friedel-Crafts Polymers. 11. Friedel-Crafts Polymers from 4,4′-Dichloromethyldiphenyl Ether and Chlorophenols

Friedel-Crafts polymers formed on polycondensation of 4,4′-dichloro-methyldiphenyl ether (DDE) with benzene, toluene, isomeric chlorotoluenes and xylenes, phenol, and isomeric cresols have been reported [1–4]. The synthesis and characterization of polymers formed on condensation of chloro-phenols with DDE are described in the present communication.     

NMR studies of the reversible and regioselective lactonization of α-2,8-linked trisialic acid in aqueous acid

The pH dependent lactonization of trisialic acid was examined using NMR and CE techniques. The combined studies indicate that lactonization is a dynamic, pH dependent process that occurs with preferential lactonization between the carbonyl of the central residue and the reducing end C-9 hydroxyl group.     

Amberlyst-15: an efficient and reusable catalyst for the Friedel-Crafts reactions of activated arenes and heteroarenes with α-amido sulfones

The heterogeneous Amberlyst-15 catalyst displays efficient catalytic properties for the Friedel-Crafts reactions between an activated arenes or heteroarenes and α-amido sulfones. Various α-amido sulfones on treatment with 1,2,4-trimethoxy benzene give the Friedel-Crafts reaction products in very good yield. The reactions with heteroarenes show moderate yield of the product. The catalyst can be easily recycled without significant loss of activity.     

Highly effective and regioselective Michael addition of indoles to α,β-unsaturated ketones promoted by pentafluorophenylammonium triflate

A simple, inexpensive, environmentally friendly and efficient route for Michael addition of indoles to α,β-unsaturated ketones using pentafluorophenylammonium triflate (PFPAT) as a catalyst is described. Various indole derivatives were synthesized in good to excellent yields. The preparation of PFPAT catalyst from simple and readily available starting materials makes this method more affordable.     

Synthesis of substituted α-tetralones and substituted 1-naphthols via regioselective ring expansion of 1-acyl-1-indanol skeleton

Substituted 1-acyl-1-indanols were prepared using the corresponding readily commercially available substituted indanones as starting materials. Treatment of each 1-acyl-1-indanol derivative with sodium methoxide in hot methanol furnished a regiospecific 2-hydroxy-α-tetralone derivative, which was an α-keto rearrangement product. Each substituted 2-hydroxy-α-tetralone then underwent dehydration to afford the corresponding 1-naphthol derivative.     

Stereo- and regioselective synthesis of β-amino-β-tetrazolylvinylphosphonates

Addition of 5-substituted tetrazoles to dimethyl [(N,N-diisopropylamino)ethynyl]phosphonate proceeds regio- and stereoselectively to yield (Z)-[2-diisopropylamino-2-(tetrazolyl)vinyl]phosphonic acid dimethyl esters. The Z-configuration of the products was confirmed by ¹Н NMR spectroscopy and single-crystal X-ray diffraction. The reactions occur via nucleophilic attack of tetrazole involving predominantly the N-1 atom of the tetrazole ring.     

An Efficient Synthetic Method to Nonnatural α- and β-Tryptophan Analogues via Friedel-Crafts Alkylation of Indoles with Nitroacrylates

The Friedel-Crafts alkylation of indoles with nitroacrylates could provide α- and β-tryptophan nitro-precursors, respectively, in moderate to good yields under Lewis acid catalysis. The diastereoselectivities of the reaction were enhanced by using 2-substituted indoles. The alkylation products could be easily transformed to nonnatural tryptophan derivatives.     

Friedel-Crafts Polymers. 6. Friedel-Crafts Polycondensation of p-Xylylerte Dibromide with Salicylic Acid and β-Resorcyiic Acid

Polymers were prepared by condensing p-xylylene dibromide separately with salicylic acid and β-resorcylic acid in the presence of anhydrous ferric chloride in dioxane. The polymer samples_were characterized by elemental analysis, by IR spectral study, by M determined by vapor pressure osmometry, by nonaqueous conducto-metric titration in pyridine, by TGA in air, and by viscosity measurements of polymer solutions in DMF. Polymeric metal chelates of Cu²⁺, Co²⁺, Zn²⁺, Ni²⁺, and Fe³⁺ with polymer samples were prepared and characterized by elemental analysis, by IR spectral study, and by TGA in air. The chelation ion-exchange properties of the polymer samples were studied by employing the batch equilibration method.     

Recyclable graphite oxide catalyzed Friedel-Crafts addition of indoles to α,β-unsaturated ketones

The Friedel-Crafts addition of indoles to α,β-unsaturated ketones, and nitro styrenes was studied with graphite oxide as catalyst. Various indole derivatives were synthesized in good to excellent yields. The preparation of graphite oxide catalyst from simple and readily available starting materials makes this method more affordable. The heterogeneous graphite oxide can be easily recovered and recycled up to five cycles without loss of activity.     

Reaction of acylsilanes with α-sulfinyl carbanions: regioselective synthesis of silyl enol ethers

The reaction of acylsilanes with α-sulfinyl carbanions such as α-lithioalkyl sulfoxide is described. The reaction proceeds to give silyl enol ethers preferentially through the initial formation of the α-silyl alkoxide intermediates. In particular, the products derived from enolizable acylsilanes were the regio-defined silyl enol ethers that cannot be obtained by usual enolization of the corresponding unsymmetrical ketones with base.