The transition-metal-catalyzed cross-coupling of aryl halides (ArÀX) with aryl metal reagents is one of the most reliable and widely applicable methods for biaryl synthesis. The catalytic cycle involves a two-electron reduction of ArÀX upon its oxidative addition to a low-valent transition metal.[1] Such a reduction is crucial for the employment of Ar À X as an electrophile in substitution reactions because Ar À X cannot undergo S N 1 or S N 2 reactions. A single-electron reduction also is effective for the activation of ArÀX, which is converted into [ArÀX] C À then into ArC with elimination of X À . [2,3] ). [5,6] Herein, we report the coupling of aryl halides with aryl Grignard reagents that does not require the aid of transition metals and goes through an S RN 1 mechanism. [7, 8] The reaction of phenylmagnesium bromide (1 a; 2 equiv) with 2-iodonaphthalene (2 m; 1 equiv) in THF at 60 8C for 24 h, after quenching with D 2 O, gave 2-deuterionaphthalene (23 %, > 95 % deuteration) and iodobenzene (16 %) in addition to a small amount (2 %) of 2-phenylnaphthalene (3 am), with 29 % conversion of 2 m (Table 1, entry 1). This result shows that I/Mg exchange giving 2-naphthylmagnesium bromide and iodobenzene predominates, but the crosscoupling also takes place. The selectivity for the crosscoupling over the I/Mg exchange was drastically improved by changing the reaction solvent from THF to toluene, although a higher temperature (110 8C) was required (Table 1, entries 2 and 3). The Grignard reagent 1 a was prepared in THF and most of the solvent was removed in vacuo, and then it was used for the reaction with 2 m in toluene at 110 8C for 24 h to give 3 am in 93 % yield.

Axially chiral dicarboxylic acid (R)-1d catalyzed reaction of diazoacetamides and N-Boc imines provided a novel organocatalytic means for the formation of enantiomerically enriched N-Boc protected trans aziridines.

FeCl(3) in combination with t-BuOOt-Bu as an oxidant was found to be an efficient catalyst for oxidation of alkylamides to α-(tert-butoxy)alkylamides. FeCl(2) and CuCl showed, respectively, almost the same and slightly lower activities compared with FeCl(3) in the tert-butoxylation of N-phenylpyrrolidone (1a), whereas no tert-butoxylated product was obtained by use of Fe(OTf)(3), RuCl(3), or Zr(OTf)(4). FeCl(3) was found to be effective also as a catalyst for the Friedel-Crafts alkylation with thus obtained α-(tert-butoxy)alkylamides. The Friedel-Crafts alkylation proceeded smoothly also in the presence of a catalytic amount of Fe(OTf)(3), RuCl(3), or Zr(OTf)(4). In contrast, FeCl(2) and CuCl, which showed certain activity toward the tert-butoxylation, failed to promote the Friedel-Crafts alkylation. Among the transition metal complexes thus far examined, only FeCl(3) showed high catalytic activities for both the oxidation and the Friedel-Crafts alkylation. The bifunctionality of FeCl(3) was utilized for the oxidative coupling of alkylamides with arenes through a tandem reaction consisting of oxidation of alkylamides to α-(tert-butoxy)alkylamides and the following Friedel-Crafts alkylation. The FeCl(3)-catalyzed oxidative coupling is applicable to a wide variety of alkylamides and arenes, though a combination of FeCl(3) with Fe(OTf)(3) was found to be effective for the reaction of arenes with low nucleophilicity. A Fe(II)-Fe(III) catalytic cycle is concerned with the tert-butoxylation, whereas a Fe(III) complex as a Lewis acid catalyzes the Friedel-Crafts alkylation.

The mechanism of the previously developed cross-coupling reaction of aryl Grignard reagents with aryl halides was explored in more detail. Single electron transfer from an aryl Grignard reagent to an aryl halide initiates a radical chain by giving an anion radical of the aryl halide. The following propagation cycle consists entirely of anion radical intermediates.

Fe(OTf)(3)-1,10-phenanthroline catalyzes oxidative coupling of arylboronic acids with benzene derivatives using t-BuOOt-Bu as an oxidant. The reaction proceeds through homolytic aromatic substitution with aryl radicals generated from arylboronic acids and t-BuO˙.

Rhodium-catalyzed asymmetric conjugate alkynylation of α,β-unsaturated ketones giving β-alkynylketones took place in high yields with high enantioselectivity. The reaction was realized by use of (triisopropylsilyl)acetylene combined with (R)-DTBM-segphos as a chiral phosphine ligand, where the sterically bulky substituents on the silicon and phosphorus atoms suppress the alkyne dimerization.

Arylzinc reagents, prepared from aryl halides/zinc powder or aryl Grignard reagents/zinc chloride, were found to undergo coupling with aryl and alkenyl halides without the aid of transition-metal catalysis to give biaryls and styrene derivatives, respectively. In this context, we have already reported the corresponding reaction using aryl Grignard reagents instead of arylzinc reagents. Compared with the Grignard cross-coupling, the present reaction features high functional-group tolerance, whereby electrophilic groups such as alkoxycarbonyl and cyano groups are compatible as substituents on both the arylzinc reagents and the aryl halides. Aryl halides receive a single electron and thereby become activated as the corresponding anion radicals, which react with arylzinc reagents, thus leading to the cross-coupling products.

The transition-metal-catalyzed cross-coupling of aryl halides (ArÀX) with aryl metal reagents is one of the most reliable and widely applicable methods for biaryl synthesis. The catalytic cycle involves a two-electron reduction of ArÀX upon its oxidative addition to a low-valent transition metal.[1] Such a reduction is crucial for the employment of Ar À X as an electrophile in substitution reactions because Ar À X cannot undergo S N 1 or S N 2 reactions. A single-electron reduction also is effective for the activation of ArÀX, which is converted into [ArÀX] C À then into ArC with elimination of X À . [2,3] ). [5,6] Herein, we report the coupling of aryl halides with aryl Grignard reagents that does not require the aid of transition metals and goes through an S RN 1 mechanism. [7, 8] The reaction of phenylmagnesium bromide (1 a; 2 equiv) with 2-iodonaphthalene (2 m; 1 equiv) in THF at 60 8C for 24 h, after quenching with D 2 O, gave 2-deuterionaphthalene (23 %, > 95 % deuteration) and iodobenzene (16 %) in addition to a small amount (2 %) of 2-phenylnaphthalene (3 am), with 29 % conversion of 2 m (Table 1, entry 1). This result shows that I/Mg exchange giving 2-naphthylmagnesium bromide and iodobenzene predominates, but the crosscoupling also takes place. The selectivity for the crosscoupling over the I/Mg exchange was drastically improved by changing the reaction solvent from THF to toluene, although a higher temperature (110 8C) was required (Table 1, entries 2 and 3). The Grignard reagent 1 a was prepared in THF and most of the solvent was removed in vacuo, and then it was used for the reaction with 2 m in toluene at 110 8C for 24 h to give 3 am in 93 % yield.