Umpolung of Indoles: Triflic Acid-Mediated C3-Regioselective Hy-droarylation of N-H Indoles

The direct dearomative addition of arenes to the C3-position of unprotected indoles is reported under operationally simple conditions with triflic acid at room temperature. The present regioselective hydroarylation is a straightforward manner to gen-erate an electrophilic indole at the C3-position without the need to introduce a deactivating acetyl group on the indolic nitrogen as in previously reported strategies. This atom economy method delivers biologically relevant 3-aryl indolines and 3,3-spiroindolines in high yields and regioselectivities from both intra and intermolecular processes.

One-Pot, Catalyst-Free Synthesis of Nitriles from Aldehydes Using Aminating Reagent MsONH3OTf

An eco-friendly protocol to synthesize nitriles from their corresponding aromatic and aliphatic aldehydes in excellent yields has been developed. This is a catalyst-free protocol which employs an aminating reagent (MsONH3OTf) under mild conditions. The hydroxylamine triflic acid salts (MsONH3OTf) acted as the N source for this protocol. Our protocol proved to be easy to perform and presented good functional group tolerance.

AlBr3-Promoted stereoselective anti-hydroarylation of the acetylene bond in 3-arylpropynenitriles by electron-rich arenes: synthesis of 3,3-diarylpropenenitriles

Reactions of 3-arylpropynenitriles (ArC≡CCN) with electron-rich arenes (Ar′H, benzene and its polymethylated derivatives) under the action of aluminum bromide (AlBr3, 6 equiv) at room temperature for 0.5–2 h result in the stereoselective formation of 3,3-diarylpropenenitriles (Ar(Ar′)C=CHCN) in yields of 20–64%, as products of mainly anti-hydroarylation of the acetylene bond. The obtained 3,3-diarylpropenenitriles in triflic acid CF3SO3H (TfOH) at room temperature for 1 h are cyclized into 3-arylindenones in yields of 55–70%.

Synthesis of 5-arylacetylenyl-1,2,4-oxadiazoles and their transformations under superelectrophilic activation conditions

Acetylene derivatives of 1,2,4-oxadiazoles, i.e., 5-(2-arylethynyl)-3-aryl-1,2,4-oxadiazoles, have been obtained, for the first time reported, from 5-(2-arylethenyl)-3-aryl-1,2,4-oxadiazoles by their bromination at the carbon–carbon double bond followed by di-dehydrobromination with NaNH2 in liquid NH3. The reaction of the acetylenyl-1,2,4-oxadiazoles with arenes in neat triflic acid TfOH (CF3SO3H) at room temperature for 1 h resulted in the formation of E/Z-5-(2,2-diarylethenyl)-3-aryl-1,2,4-oxadiazoles as products of regioselective hydroarylation of the acetylene bond. The addition of TfOH to the acetylene bond of these oxadiazoles quantitatively resulted in E/Z-vinyl triflates. The reactions of the cationic intermediates have been studied by DFT calculations and the reaction mechanisms are discussed.

Synthesis of 5-arylacetylene 1,2,4-oxadiazoles and their transformations under superelectrophilic activation conditions

Acetylene derivatives of 1,2,4-oxadiazoles, 5-(2-arylethynyl)-3-aryl-1,2,4-oxadiazoles, have been obtained, for the first time, from 5-(2-arylethenyl)-3-aryl-1,2,4-oxadiazoles by their bromination at the carbon-carbon double bond followed by di-dehydrobromination with NaNH2 in liquid NH3. Reaction of the acetylene 1,2,4-oxadiazoles with arenes in neat triflic acid TfOH (CF3SO3H) at room temperature for 1 h result in the formation of E-/Z-5-(2,2-diarylethenyl)-3-aryl-1,2,4-oxadiazoles as products of regioselective hydroarylation of the acetylene bond. Addition of TfOH to acetylene bond of these oxadiazoles gives rise quantitatively to E-/Z-vinyl triflates. Reaction cationic intermediates have been studied by DFT calculations. The reaction mechanisms have been discussed.