The generation of iminium ions using chlorosilanes and their reactions with electron rich aromatic heterocycles

Abstract

Dichlorodimethylsilane and trichloromethylsilane have been used to generate iminium ions from aminals and aminol ethers derived from secondary alkylamines, including glycine derivatives, in aprotic media which were shown to undergo reactions with electron rich aromatic heterocycles, including furan, to give mono-aminoalkylation products in good yields. Whereas chlorotrimethylsilane has been shown to generate iminium ions from aminol ethers, no evidence was adduced for the involvement of iminium ions using aminals. 2,5-Disubstitution of N-methylpyrrole was the major result in reactions of N-methylpyrrole with aminals in the presence of chlorotrimethylsilane where no build up of hydrogen chloride occurs and where chlorotrimethylsilane can function catalytically. Experimental results, including the use of bis(trimethylsilyl)acetamide as a proton scavenger, and some relative rate data, are presented that allow possible mechanisms to be evaluated.