Palladium-Catalyzed Cross-Methylation of Haloarenes Possessing Active Hydrogen Atoms by Intramolecularly Stabilized Dimethylindium and Dimethylaluminum Reagents

While the intramolecularly stabilized aluminum complex [(CH3)2AlOCH2CH2N(CH3)2]2 (2a) reacts readily with 4-bromophenol to give methane and [(4-BrC6H4O)2AlOCH2CH2N(CH3)2]2 (7), the demethylation of the analogous indium complex [(CH3)2InOCH2CH2N(CH3)2]2 2c is very slow. This inertness of 2c enables it to cross-methylate bromophenols and other bromoarenes with active hydrogen atoms in the presence of soluble palladium phosphane catalysts. The cross-methylation by 2c can be carried out under an ambient atmosphere. The ring-bound bromine atoms in 7 are replaced by CH3 groups when treated with an excess of the methylation reagent 2a, and the resulting aluminum cresolate liberates 4-methylphenol upon hydrolysis. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)