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

Abstract

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%.

DFT insights into superelectrophilic activation of α,β-unsaturated nitriles and ketones in superacids

“…9,11,[30][31][32] It is not surprising, therefore, that these and analogous species have been repeatedly proposed as key superelectrophilic 2 intermediates in the corresponding reactions with weak nucleophiles, such as benzene, deactivated aromatics and alkanes. 6,[8][9][10][11][12][13][14][15][16][17][18][19][20][22][23][24][25][26]33 On the other hand, perhaps the most widely proposed candidate for the role of a strong electrophile derived from α,β-enones in superacids is the O,O-diprotonated form 6 (Fig. 4).…”

“…undergo a specific kind of electrophilic activation upon action with strong Brønsted or Lewis acids. 1–25 This allowed involving them in a large variety of Friedel–Crafts type transformations, offering quite appealing synthetic solutions. Fig.…”

“…9,11,30–32 It is not surprising, therefore, that these and analogous species have been repeatedly proposed as key superelectrophilic 2 intermediates in the corresponding reactions with weak nucleophiles, such as benzene, deactivated aromatics and alkanes. 6,8–20,22–26,33…”

“…26,42–44 In addition, hypothetical complexes 11 and 12 , in which carbon–carbon double bonds are directly coordinated to aluminium chloride, may also be considered as intermediates of enhanced electrophilicity. 15,24 Their likely involvement seems reasonable, given, among other things, that they do not require protonic acid at all.…”