PALLADIUM-CATALYZED METHYLATION OF ARYL AND VINYL HALIDES BY STABILIZED METHYLALUMINUM AND METHYLGALLIUM COMPLEXES

The intramolecularly stabilized mono-and dialkylaluminum complexes la, 2, 3, 4a, 5a, 5c, 6a, 6c, 7, 8, and 9 in the presence of palladium ca talysts, cross-alkylate aryl, vinyl, and benzyl bromides and iodides u nder mild standard laboratory conditions. Aryl bromides with carbonyl substituents or benzylic halides are converted partially into dialkyl compounds. Under similar conditions, the analogous stabilized dimethyl gallium complexes Ib, 4b, 5b, 6b, and 10 methylate aryl and vinyl brom ides and iodides in a highly selective manner. Substituted bromobenzen es XC6H4Br, where X = CHO, COPh, CO2Et, CN, NO2, Cl, CH2Br, or CH=CHCO Ph, are methylated by the organogallium reagents usually only at the a romatic ring halogen atom to give substituted toluenes as single produ cts. The methylation rates were shown to depend on the nature of the c helating ligands, on the solvent, and on the type of palladium catalys t employed.