Transition-metal-free cross-coupling reaction of benzylic halides with arylboronic acids leading to diarylmethanes

Vinylation of Benzylic Amines via C–N Bond Functionalization of Benzylic Pyridinium Salts

“…These results show that a metal-free pathway is possible, but not as effective as the reaction involving the nickel catalyst. Based on previously reported metal-free vinylations, 8g, 13 we hypothesize the metal-free variant proceeds via nucleophilic attack of a vinyl boronate to the benzylic pyridinium ion, likely in an S N 2 fashion. With PhenNi(OAc) 2 ·xH 2 O present, a Ni I/III (or Ni 0/II ) catalytic cycle may also operate, but we cannot exclude the possibility that nickel acts as a Lewis acid with our current data.…”

“…6 In addition, 1,3-diaryl allylic molecules themselves can posses promising biological activity. 7 By harnessing a benzylic amine, this method offers synthetic opportunities that are complementary to analogous cross-couplings of benzylic halides 8 and alcohol derivatives, 9 as well as umpolung strategies that utilize benzylic nucleophiles. 10,3k, 11, 11l, 12,8g, 13 Specifically, many previous cross-couplings of benzylic substrates largely neglect heteroaryl substitution.…”

“…10,3k, 11, 11l, 12,8g, 13 Specifically, many previous cross-couplings of benzylic substrates largely neglect heteroaryl substitution. 8a, 8d, 11n, 11w, 11ab, 14…”

“…Furthermore, although lower yielding than the reactions with a nickel catalyst, a transition metal-free pathway was also observed for this vinylation. 8g, 13…”

Electron‐Catalyzed Cross‐Coupling of Arylboron Compounds with Aryl Iodides

“…[9,10] Herein, we report for the first time that arylboron compounds can be utilized as aryl nucleophiles in the electron-catalyzed crosscoupling with the aid of az inc reagent such as diethylzinc or zinc chloride/potassium tert-butoxide. [11] Many reports are available on the preparation of arylzinc reagents from arylboronic acids through treatment with an excess of diethylzinc. [12,13] We anticipated that the thus prepared arylzinc reagents would undergo the electroncatalyzed cross-coupling.H owever,t reatment of phenylboronic acid (1a,2equiv) with Et 2 Zn (6 equiv) in THF at 23 8 8C for 1h followed by reaction with 4-iodoanisole (2a)i n toluene/THF (1:3) at 110 8 8Cf or 24 hf ailed to give the corresponding coupling product, 4-methoxybiphenyl (3aa), at all, with alow conversion of 2a (Table 1, entry 1).…”