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...
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The reactions between meso-disubstituted dipyrromethanes and titanium and zirconium amides and alkyls have generated the first examples of dipyrrolide complexes of Group 4 metals.
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