An extremely technically simple crossmethylation of aryl and vinyl halides and pseudohalides using an air-stable adduct of trimethylaluminium with a Pd(0) catalyst supported by commercially available biarylphosphines gives excellent yields of methylated products (mainly > 95%). Reactions can be run with either 0.5 mol % catalyst or without requiring the exclusion of atmospheric oxygen or the drying of solvents in some cases. A wide variety of functional groups is tolerated including CN, OH, CO 2 R, CHO and NO 2 .Keywords: alkylation; aluminium; aryl halides; crosscoupling; palladium; vinyl halides Palladium-and nickel-catalysed cross-alkylation of aryl and vinyl halides or pseudohalides with organometallic reagents represents an extremely powerful method of C À C bond formation.[1] A major drawback of this chemistry is often the air-sensitive nature of the organometallic reagents used. While tremendous developments have taken place in the use of organoboron [2] and organosilicon reagents, [3] the utility of air-stable organometallic reagents capable of transferring alkyl C(sp 3 ) nucleophiles, especially a simple CH 3 group, is relatively unexplored. Attempts to realise stabilised reagents derived from trimethylaluminium through the formation of Lewis acid/ base pairs have been reported by Schumann, Blum and co-workers leading to the reagents 2 and 3 (among others).[4] While the use of 2 and 3 under nickel or palladium catalysis gives synthetically viable yields of the methylated products, starting from aryl halides, both 2 and 3 must be handled under inert atmospheres.[5] Recently, we demonstrated that the remarkably air-stable AlMe 3 adduct (AlMe 3 ) 2 · DABCO (DABCO ¼ 1,4-diazobicyclo[2.2.2]octane) (1), which we call DABAL-Me 3 , [6] could be applied to the asymmetric methylation of aldehydes.[7] DABAL-Me 3 (1), formed in one step from DABCO and neat AlMe 3 , although somewhat moisture sensitive can be easily handled without the need for an inert atmosphere. In comparison to the SchumannBlum reagents 2 and 3 DABAL-Me 3 (1) is prepared directly from inexpensive, commercially available materials and is an extremely convenient source of methyl carbanions. Herein we report a convenient, robust and near quantitative method for the Pd-catalysed cross-methylation of aryl and vinyl halides or pseudohalides which utilises the reagent 1.Preliminary work demonstrated that in the presence of 3 mol % Pd(PPh 3 ) 4 , in anhydrous THF at reflux and under an inert atmosphere, synthetically useful yields of methylated products are attained from the cross-alkylation of DABAL-Me 3 (1) using unfunctionalised aryl bromides and iodides (50 -96%). However, in practice separation of the starting halides from their methylated products is not easily attained in preparative procedures and we sought to attain a process resulting in complete conversions and near quantitative yields under mild conditions. Simple in situ generation of the catalyst allowed the screening of the commercially available 1,1'-biphenylphosphines L1 -L4. P...
Highly stereoselective 1,2-additions of AlMe3 or its air-stable analog DABCO(AlMe3)2 to aldehydes are realized in the presence of a Ni(acac)2-derived catalyst using phosphoramidite ligands giving sec-alcohols in up to 95 % ee. Very high turnover number (TON) (>1500) and turnover frequency (TOF) (>350 h-1) values can be realized in these reactions. The substrate range, trials of various (DABCO)a(AlR3)b reagents (a = 0.1; b = 1.2; R = Me, Et, Bui), ligands, and molecular modeling studies are used to propose a working model for the catalytic cycle and the origin of the stereoselectivity. The phosphoramidite ligand is proposed to bind the nickel in an η2 manner via the P-donor and one of the C=C aryl bonds of the CHAr amine group. Preliminary studies indicate that DABCO(AlMe3)2 can also be used as a methyl source in Pd-catalyzed cross-coupling reactions of ArX (X = Br, I) species.
The oxidation of toluene by cobaltic perchlorate in 50% aqueous methyl cyanide is a slow reaction, substantially of the first order with respect to both [CoII'] and [PhMe], which yields mainly benzaldehyde and benzoic acid together with traces of benzyl alcohol and bibenzyl. Faster oxidation of the toluene occurs in the presence of propionic, isobutyric, and pivalic acids, all of which concurrently oxidise. This induced oxidation of toluene is ascribed to the production of alkyl radicals from the carboxylic acids, i.e.,
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