Enamines in the synthesis of 2-(substituted amino)-3,3-dialkylchromanones

Abstract

Ethanamines with two alkyl groups at position 2 react with derivatives of 2-hydroxybenzaldehyde to give 2-alkylamino-3,3-dialkylchroman-4-ols such as (4a) as mixtures in which one diasteroisomer preponderates. Oxidation supplies the corresponding chromanones of type (4b) as single racemates except for the bischromanone derived from piperazine. The enamines used were derived from morpholine, pyrrolidine, N-methylaniline, and piperazine as bases, and 2-methylpropanal, 2-methylbutanal, and cyclohexanecarbaldehyde as carbonyl components. 2-Hydroxybenzaldehyde itself, and its 3-methoxy-, 4-methoxy3,5-dibromo-, 4,6-dimethyl-, 5-nitro-, and 3-nitro-derivatives, and also 2-hydroxynaphthalene-1-carbaldehyde were employed.