Superacid-catalyzed preparation of aryl-substituted piperidines via dicationic electrophiles

Palladium-Catalyzed Arylation of Endocyclic 1-Azaallyl Anions: Concise Synthesis of Unprotected Enantioenriched cis-2,3-Diarylpiperidines

Unprotected cis-2,3-diarylpiperidines are synthesized through an unprecedented palladium-catalyzed cross-coupling reaction between aryl halides and elusive endocyclic 1-azaallyl anions. These intermediates are generated in situ by the deprotonation of 2-aryl-1-piperideines, precursors that are readily prepared in two operations from simple piperidines. An asymmetric version of this reaction with (2R, 3R)-iPr-BI-DIME as the ligand provides products in moderate to good yields and enantioselectivities. This study significantly expands the synthetic utility of endocyclic 1-azaallyl anions.

Superelectrophilic Csp3-H bond fluorination of aliphatic amines in superacid: the striking role of ammonium-carbenium dications

The superacid-promoted electrophilic Csp3-H bond activation of aliphatic amines generates superelectrophilic species that can be subsequently fluorinated. Demonstrated by low-temperature in situ NMR experiments, the ammonium-carbenium dications, crucial for this reaction, can also react with C-H bonds opening future synthesis perspectives for this mode of activation.

Anti-Markovnikov rearrangement in sulfur mediated allylic C-H amination of olefins

Cationic rearrangement reactions usually follow Markovnikov's rule to give more substituted carbocations as stable intermediates. During our study on sulfur mediated allylic C-H amination of olefins, very rare cases of anti-Markovnikov rearrangement from secondary carbocations toward primary carbocations or primary triflates were observed.

A novel, facile route to β-fluoroamines by hydrofluorination using superacid HF–SbF5

A range of unsaturated amines and sulfonamides were converted to beta-fluoro nitrogen analogues after hydrofluorination in superacid HF-SbF(5), based on the formation of highly reactive electrophilic intermediates.

Superacid-Catalyzed Reactions of Cinnamic Acids and the Role of Superelectrophiles1

The chemistry of cinnamic acids and related compounds has been studied. In superacid-catalyzed reactions with arenes, two competing reaction mechanisms are proposed. Both mechanisms involve the formation of dicationic intermediates (superelectrophiles), and the reactions can lead to either chalcone-type products or indanone products. The direct observation of a dicationic species (by low-temperature (13)C NMR) is reported. We provide clear evidence that protonated carboxylic acid groups (or the corresponding acyl cation) can enhance the reactivity of an adjacent electrophilic center. Triflic acid is also found to be an effective acid catalyst for the direct synthesis of some electron-deficient chalcones and heterocyclic chalcones from cinnnamic acids.

Dicationic electrophiles from olefinic amines in superacid

This paper describes the superacid-catalyzed chemistry of olefinic amines and related compounds. A variety of olefinic amines are found to react with benzene in CF(3)SO(3)H (triflic acid) to give addition products in good yields (75-99%), including the pharmaceutical agents fenpiprane and prozapine. A general mechanism is proposed that invokes the formation of reactive, dicationic electrophiles and the direct observation of a diprotonated species is reported from low-temperature NMR experiments. This chemistry is also used to conveniently prepare functionalized polystyrene beads having pendant amine groups.

Chemistry of dicationic electrophiles: superacid-catalyzed reactions of amino acetals

Amino acetals are shown to form highly electrophilic systems in Bronsted superacids. It is proposed that amino acetals give dicationic electrophiles, and this proposal is supported by the direct observation of a dication by low-temperature (13)C NMR. When reacted with C(6)H(6) and superacidic CF(3)SO(3)H, amino acetals are shown to provide 1-(3,3-diphenylpropyl)amines and 1-(2,2-diphenylethyl)amines as condensation products in good yields (50-99%).