Exhaustive C-methylation of carboxylic acids by trimethylaluminium: A new route to t-butyl compounds

Abstract

Carboxylic acids are exhaustively C-methylated to t-butyl compounds by excess trimethylaluminium at c. 120º. Benzoic acid for example, gives t-butylbenzene. Similarly methylated are o-fluoro-, o-bromo-, and m-chloro-benzoic acids, 5-chloro-3-phenylsalicylic acid, 1-naphthoic acid, palmitic, oleic and undec-10-enoic acids. Adamantane-1-carboxylic acid gives mostly l-isopropenyladaman- tane, along with some 1-t-butyladamantane. Cinnamic acid gives mainly the allylically rearranged 2-methyl-4-phenylpent-2-ene. Triphenylacetic acid behaves atypically; 1,1,1-triphenylpropan-2-one and 3,3,3-triphenylpropyne result.