α-haloenol acetates:: Versatile reactants for oxetan-2-one, azetidin-2-one and isoxazolidin-5-one synthesis

New ketene equivalents, namely alpha-haloenol acetates, are investigated as both nucleophilic and electrophilic reactants in a tandem aldol-lactonization reaction. Diethylaluminurn ethoxide proves to be an efficient promoter for the aldol reaction with a wide range of substrates, including inter alia, aldehydes, ketones, imines, nitrones and oximes, leading to oxetan-2-ones, azetidin-2-ones and isoxazolidin-5-ones. The resultant heterocyclic adducts are common structural elements in numerous compounds of interest as well as key intermediates in the preparation of other functionalities. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).