Stereochemistry of the tetrahydroquinolines from the condensation of methylaniline and glycolaldehyde

Abstract

N-Methylaniline reacts with hydroxyethanal in ethanol at 20 °C to give 3a-hydroxy-2α-hydroxymethyl-1-methyl-4β-(N-methylanilino)-1,2,3,4-tetrahydroquinoline (6), the structure of which has been established by X-ray crystal structure analysis. The heterocyclic ring adopts a C₃-sofa conformation in which the methylanilino residue and the hydroxy group are equatorial and the hydroxymethyl group is axial. The dioi (6) readily undergoes thermal or acid-catalysed elimination of methylaniline to give the bridged tetrahydroquinoline (9).