C-Methylation of alcohols by trimethylaluminium

Abstract

Tertiary alcohols and aryl alkyl carbinols are C-methylated by excess trimethylaluminium, mostly at temperatures in the range 100-200�. Thus t-butyl alcohol gives neopentane, 1,l-diphenylethanol gives 2,2-diphenylpropane, 2-phenylpropan-2-ol gives t-butylbenzene, and tri-p-ethoxyphenyl- methanol gives l,l,l-tri-p-ethoxyphenylethane. 1-Methyladamantane is obtained from adamantan-1-ol and excess trimethylaluminium or by pyrolysis of dimethylaluminium 1-adamantyl oxide. l,l,l-Triphenylethane is obtained from tri-phenylmethanol and excess trimethylaluminium (at temperatures as low as 60�), by pyrolysis of dimethylaluminium triphenylmethoxide, or by reaction of triphenylmethyl dimer with various methylmetallic compounds. Catalysis and other mechanistically significant features of the new 'exhaustive methylation' are discussed, and experimental procedures for the use of alkylaluminium compounds in the organic laboratory are described.