Stereochemistry of the quaternization of 2- and 4-epimeric trans-1-alkyl-2-methyl-4-ethynyldecahydro-4-quinolols with alkyl halides

Abstract

The quaternization of trans-1-alkyl-2-methyl-4-ethynyldecahydro-4-quinolols containing an equatorial 2-CH₃ group by means of methyl iodide proceeds with predominant axial incorporation of the methyl group, whereas quaternization of the corresponding trans-1,2-dimethyl-4-ethynyldecahydro-4-quinolols by means of ethyl and n-propyl iodide takes place with predominant equatorial incorporation of the alkyl group; the ratios of the stereoisomers in the products of forward and reverse quaternization are approximately identical. Methylation of amino alcohols with an axial 2-CH₃ group also leads to the predominant formation of epimers of the quaternary salts with an axial methyl group attached to the nitrogen atom, whereas the reverse quaternization of these amino alcohols proceeds nonstereoselectively to give an approximately equimolar mixture of the epimers of the quaternary salts.