Domino Reactions of Chromones with Heterocyclic Enamines
Peter Langer
Abstract
Abstract Domino reactions of heterocyclic enamines with chromone derivatives provides a convenient synthesis of a great variety of annulated heterocyclic ring systems. The course of the reaction depends on the type of substituent located at position 3 of the chromone. Reactions of 3-unsubstituted chromones, 3-nitrochromones, and 3-halochromones proceed by conjugate addition of the carbon atom of the enamine to carbon C-2 of the chromone, ring cleavage, and recyclization via the chromone carbonyl group. In the case of 3-formylchromes, 3-dichloroacetylchromone, 3-perfluoroalkanoylthiochromones, 3-(2-fluorobenzoyl)chromones, and 3-methoxalylchromones the final cyclization proceeds via the carbonyl group located outside the chromone moiety. The functional groups located at the carbonyl group at position 3 of the chromone allow for further synthetic transformations including additional ring closures. Contents 1 Introduction 2 3-Unsubstituted Chromones 3 3-Nitrochromones 4 3-Formylchromes 5 3-Dichloroacetylchromone 6 3-Perfluoroalkanoylthiochromones 7 3-Methoxalylchromones 8 3-(2-Fluorobenzoyl)chromones 9 3-Halochromones 10 Chromone-3-carboxylic Acids 11 Conclusions