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DOI: 10.1055/sos-SD-040-00344

Lawrence, S. A.Science of Synthesis, (200940518.

Generally, when a quaternary ammonium salt is heated with another amine of sufficient nucleophilicity N-dealkylation takes place. Thus, heating alkyltrimethylammonium iodides in a 10- to 15-fold molar excess of 2-aminoethanol at 154°C gives alkyldimethylamines along with alkene elimination products.[‌71‌] This reaction is synthetically useful for monodealkylation of cyclic 1,1-dialkylpiperidinium or 1,1-dimethylhexahydro-1H-azepinium salts (Scheme 27), but ring opening can compete in the case of pyrrolidinium salts. In any case, demethylation is particularly fast so that potentially an N-methyl group can be substituted by a higher alkyl chain in a sequence of N-alkylation and demethylation.[‌72‌] A drawback of the use of 2-aminoethanol is the possible cleavage of methoxy groups and of ester groups.[‌73‌]

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