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˙.