(S)-(–)-Proline Catalysed Alkylation of 1,3-Dihydroxyanthraquinone with Phenylacetaldehyde

Abstract

In the presence of the amino acid (S)-(-)-proline, 1,3-dihydroxyanthraquinone (1) is alkylated by phenylacetaldehyde to give an anomeric mixture of lactols (2). The lactols are oxidized to the corresponding lactone (3) by manganese dioxide or chromic acid. Treatment of (2) with p-toluenesulfonic acid yields the expected enol ether (4) along with the substitution product (5). Mass spectrometry fragmentation, high-resolution ¹H N.M.R. and ¹³C n.m.r, studies of these compounds are discussed.