Barbier-type allylation of carbonyl derivatives by use of aluminum as an electron pool. Double allylation of carboxylic esters

Double allylation of carboxylic esters with allyl bromide was performed successfully by the action of aluminum metal and a catalytic amount of lead(II) bromide in tetrahydrofuran (THF). The proper choice of solvent is essential for the reaction; thus, among the examined solvents, ethers, e.g. THF, 1,2-dimethoxyethane (DME), and diethyl ether, could be successfully used for the double allylation but with N,N-dimethylformamide (DMF), aqueous MeOH, and aqueous THF, no appreciable reaction occurred. Allylation of benzaldehyde dimethyl acetal and N-benzylimine in THF under the same conditions took place smoothly to afford the corresponding allylation products. In a similar manner, allylation of benzonitrile was also performed to afford the doubly allylated benzylamine.