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The solid acid, tin hydroxide-embedded montmorillonite, catalyzes the unprecedented alkylation of various silicon enolates with primary, secondary and tertiary benzylic alcohols as well as secondary allylic alcohols. The acid catalysis of Sn-Mont was not only higher than that of the other ion-exchanged montmorillonites (M-Mont; M = H, Ti, Fe and Al), but also higher than that of the typical homogeneous acid catalysts such as BF 3 ·OEt 2 , TMSOTf and TfOH.

Fully protected pyrazolidines can be readily obtained by acid-catalysed cyclisations of the corresponding allylic hydrazines by carbenium ion generation using concentrated sulfuric acid in dichloromethane.

A method for regioselective alkylation of the 3-thiono-1,2,4-triazinone 10 at the sulfur atom is reported. Subsequent Claisen rearrangements, triggered either thermally or using a palladium catalyst, deliver N-alkylated products 13, while acid-catalysed rearrangements of examples where a tertiary carbenium ion can be generated, result in the formation of N-thioalkyl derivatives.

Dehydration of ethyl 3-hydroxyquinuclidine-3-carboxylate is one of the key steps during production of the antihistamine drug Quifenadine (Phencarol). The side products of this process were isolated and their structures proved using NMR spectroscopy. Carbenium ion rearrangements of quinuclidine-3-carboxylate gave rise to 1-azabicyclo[3.2.1]octane and 5-azatricyclo[3.2.1.02,7]octane systems, which serve as impurity standards for the manufacturing process of Quifenadine and are also interesting building blocks for medicinal chemistry.

Esters are chemical compounds with many practical uses. The common type of esterification is called the Fischer esterification. Another one is by the action of acid chlorides on alcohols but not with tertiary alcohols. The stable carbenium ions formed from tertiary alcohols favor elimination and the byproduct, hydrogen chloride prevents ester formation. In this new report, palladium inserted ArCOPdCl species reacts with tertiary alcohols and cross-coupling under microwave heating, minimizes the formation of probable carbenium ion, and promotes successful production of highly substituted esters in good to high yields.

A one-step synthesis of the stable [4]helicenium dye, 1,13-dimethoxy-chromeno[2,3,4- kl ]xanthenium hexafluorophosphate (DMCX + ) from the readily available tris(2,6-dimethoxyphenyl)carbenium ion is reported. The crystal structure, the chemical stability, and dye properties of the DMCX + helicenium system are described.

A novel, acid catalyzed rearrangement of the 11-trimethylsilyl-tetracyclo[8.1.0.0 3,7 .0 4,11 ]undeca-5,8-diene ring system was observed. The trimethylsilyl substitution on the cyclopropane moiety was found to be crucial for rapid, high yielding formation of the unusual homotriquinacene ring system. The transformation is presumed to proceed via a series of carbenium ion intermediates that can be trapped with suitable nucleophiles.

A new, short total synthesis of dihydroactinidiolide 1 is described using selenium carbenium ion-promoted carbon–carbon bond formation as the key step. Our synthetic strategy starts with a lactonization reaction between 1,3,3-trimethylcyclohexene 13 and α-chloro-α-phenylseleno ethyl acetate 14, affording the key intermediate, α-phenylseleno-γ-butyro lactone 15, which reacted via a selenoxide elimination to the target compound 1.

Addition of carbon disulfide to 2-isopropylidene- and 2-methylene-1,3-dimethylimidazolidines gave the thermally stable, crystalline inner salts, 1,3-dimethylimidazolidiniodithioacetates (10 and 12), where carbenium ion and dithiocarboxylate parts are insulated by an sp3 carbon atom. X-Ray diffraction analyses of these compounds and the reaction of 10 with DMAD are described.

Bis(diethylamino)[(methylthio)thiocarbonyl]carbenium salts (1), a carbenium ion carrying an α-thiocarbonyl group, shown ambident reactivities toward a series of nucleophiles. Thus, they reacted with a typically hard nucleophile, hydroxide, at the carbenium carbon atom, whereas they smoothly reacted with soft nucleophiles, such as carbon, nitrogen, sulfur, and phosphorus nucleophiles, at the thiocarbonyl sulfur atom.

Monosilylation of 1,2-thiazetidine 1,1-dioxides (β-sultams) furnished (3R ∗ , 4S ∗ )-4- silylated β-sultams stereoselectively. Treatment of 4-silylated β-sultams with a Lewis acid caused the selective CN bond cleavage because of the β-silyl stabilization against the resultant carbenium ion followed by desilylation to provide (E)-vinylsulfonamides stereospecifically.

A novel route for assembling cyclopent-[a]indene framework bearing useful functionalities has been developed through bis(methylthio) carbenium ion mediated Lewis acid induced tandem cyclization of bis-(methylthio) methylene aryl cyclopropyl ketones 1b – d and the corresponding carbinols 11b–d .

Rate constants for the reactions of the bis(p-dimethylaminophenyl)carbenium ion 1 with silyl enol ethers, allyl silanes, and allyl stannanes show the reactivity order H2C=CR-CH2SiMe3 < H2C=CR-OSiMe3 < H2C=CR-CH2SnBu3.

The AM1 results of the relative reactivity and the angle of deviation from the coplanarity between developing carbenium ion and the benzene π-system in the TS for S N 1 reactions of α-t-butylbenzyl systems agree well with those of the experimentally observed.

The title carbenium ion 1 was observed by low temperature NMR in solution. Its strong oxidizing power was demonstrated by the reduction potential and the effective oxidation of methoxy-substituted benzopinacolone 3 .

The ability of the azido group to stabilize an α carbenium ion was calculated to be intermediate between that OH and NH 2 . The barrier for the decomposition of the title compound into N 2 and H 2 CN + is 4.6kcal/mol.

The reaction of tri-2-thienylcarbenium perchlorate ( 2 ) with hydrogen and carbon nucleophiles affords three types of addition products which arise from the addition of nucleophiles at the carbenium ion center and the 3- and 5-positions of the 2-thienyl group.

Lewis acid catalyzed rearrangement of α,β-epoxy oximes proceeds by oxirane cleavage α to the oxime moiety with an attendant pinacol type alkyl migration to the resonance stabilized carbenium ion at C α , affording a 1,3-diketo-monoxime.

Phenylsulfinyl carbenium ion, generated by the acid-catalyzed decomposition of phenyl diazomethyl sulfoxide or the silver-assisted solvolysis of phenyl iodomethyl sulfoxide, is trapped by hydroxylic solvents to yield phenyl methyl sulfone. The possibility of the intermediacy of either phenylsulfinyl carbene or phenylsulfinylmethyl acetate has been ruled out.

The rate-retarding effect of ?-trifluoromethyl group observed in the solvolysis of 1-aryl-1-(trifluoromethyl)ethyl tosylates is so profound that a very large negative α + value, −8.82, is resulted and the 1-phenyl derivative becomes even less reactive than benzyl tosylate.

The k/αk isotope effect for addition of ArSCI to p-methylstyrene is small and unchanged by addition of LiClO ; k/βk is high and unchanged. For styrene and p-chlorostyrene k/βk values are high and unchanged, while k/αk increases from ∼ 1.025 to ∼ 1.04. p-Methylstyrene reacts through an open carbenium ion and the other two have cyclic intermediates.

The dicobalt hexacarbonyl complex of the enyne isopropenylacetylene ( 1 ) is effective in permitting stepwise Ad E reactions to the double bond of 1 via stabilization of the intermediate carbenium ion.

1,2-Ethanedithiol and 1,3-propanedithiol were treated with perchloric acid in acetic anhydride to give 2-methyl-1,3-dithiolan-2-yl and 2-methyl-1,3-dithian-2-yl perchlorates, respectively, which were converted to ketene dithioacetals by deprotonation with tertiary amines.