Catalyst- and oxidant-free electrooxidative site-selective [3/4 + 2] annulation to fused polycyclic heteroaromatics

Abstract

Annulation π-extension of arenes with alkynes is a straightforward and practical strategy for the rapid construction of polycyclic aromatic compounds. Recently, some intriguingly transition-metal-catalyzed polycyclic arene syntheses were described. However,...

Electro-catalytic multicomponent reaction toward asymmetrical biaryls through heteroarylation of in situ generated fused polycyclic heteroaromatics

“…The result revealed that 1 might be firstly oxidized and then underwent radical addition with 2 , which was similar to our previous study. 15 And, the oxidative potentials of intermediates 35 and 36 were found 1.27 V and 1.13 V, which indicated that 1 reacted with 2 to form an intermediate with a lower oxidation potential, which was further oxidized (Fig. 2).…”

“…Recently, a straightforward and practical electrochemical synthesis strategy for the production of fused polycyclic heteroaromatic compounds through annulative π-extension of unfunctionalized arenes with alkynes was reported by us. 15 These fused polycyclic heteroaromatic compounds with π-conjugated systems have excellent photoelectric properties and have extensive application prospects in many fields. 3 c ,16 With our continued interest in electrochemical oxidative cross-coupling with hydrogen evolution, some electrochemical coupling reactions to construct new C–C 17 bonds have been previously reported by us.…”

“…However, both [4 + 2] and [3 + 2] cyclization products were produced when 2-phenylimidazo[1,2- a ]pyridine was involved. 15 In this context, we wondered whether the single product could be obtained through the site-selective cyclization and C–H/C–H cross-dehydrogenative coupling. To our delight, the [3 + 2] cyclization intermediate could be selectively generated (Table S1†).…”

Electrochemical oxidative intramolecular annulation of aryl phosphine compounds: an efficient approach for synthesizing π-conjugated phosphonium salts

“…As an efficient, mild, eco-friendly method, organic electrochemical synthesis offers a directed oxidative route for organic substrates under oxidant-free conditions and has received continuous attention. Organic electrochemical synthesis has been utilized to achieve the C-H activation/annulation, [22][23][24][25] the construction of polycyclic aza-fused arenes [26][27][28][29] and polycyclic S-containing arenes, 30 and the electrochemical transformation of phosphorus compounds have also been reported. [31][32][33] With our continuous interests in electrochemistry [34][35][36][37][38][39] and multiple C-H activations and annulation 19,40 , herein, we report a versatile electrochemical oxidative method under oxidant-free conditions to produce fused polycyclic phosphonium salts via the C-H activation/annulation of aryl phosphine compounds (Scheme 1d), and metals and oxidants could be readily avoided in this strategy.…”

Electrochemically Promoted [3 + 2] Annulation of Imidazo[1,2-a]pyridine with Alkynes

“…We speculated that electrochemically promoted metal-free procedures might also be feasible through a radical pathway. The key features of such an annulation protocol are (1) the excellent control of regioselectivity in terms of the asymmetric internal alkyne, (2) metal- and chemical-oxidant-free conditions, and (3) the tolerance of various functional groups (Scheme c) …”