Enantioselective sequential transformations by use of metal complexes: Tandem‐Knoevenagel‐hetero‐Diels–Alder reactions with new chiral Lewis acids

Enantioselective reaction of the aldehydes 1a‐g and the 1,3‐dicarbonyl compound 2 in the presence of the chiral Lewis acid 5, derived from diacetone glucose, leads in a sequential transformation consisting of a Knoevenagel condensation and an intramolecular Diels Alder reaction to the cycloadducts 4a‐g with an ee value up to 88%. The selectivity is strongly dependent upon the temperature and solvent giving best results at room temperature in isodurene; in agreement with the principle of isoinversion, the ee values decrease at lower and higher temperatures.