Meldrum's acid in organic synthesis. V. Versatile one-pot synthesis of indolepropionic esters via simultaneous condensation of three different carbon components, indole, aldehydes and Meldrum's acid.

Abstract

When an acetonitrile solution of Meldrum's acid (1), indole (5), and an aliphatic or aromatic aldehyde (8) in the presence of a small amount of proline (except in the case of acetaldehyde) was allowed to stand at 30°C, a simultaneous condensation of three different carbon components occurred readily to give a 5-(1H-indol-3-ylalkyl)-2, 2-dimethyl-1, 3-dioxane-4, 6-dione (11) in high yield. The reaction proceeded regardless of the nature of the aldehyde. An ethanolysis of 11 with loss of acetone and carbon dioxide took place smoothly in boiling ethanol-pyridine (1 : 10) containing a small amount of copper powder to give an ethyl β-alkylindolepropionate (2). These two reactions, the condensation and the ethanolysis, were combined in a one-pot procedure, which may provide an efficient and convenient synthetic method for various ethyl indolepropionates (2).