Issue in Honor of Prof. Lutz F. Tietze ARKIVOC 2007 (v) 67-78
Gold catalysis in organic synthesis: efficient intramolecular cyclization of .-acetylenic carboxylic acids to 5-exo-alkylidene-butyrolactones
Emilie Genin, Patrick Y. Toullec, Peggy Marie, Sylvain Antoniotti, Célia Brancour, Jean-Pierre Genêt,* and Véronique Michelet*
Laboratoire de Synthèse Sélective Organique et Produits Naturels, E.N.S.C.P., UMR 7573, 11 rue P. et M. Curie, F-75231 Paris Cedex 05, France E-mail: jean-pierre-genet@enscp.fr, veronique-michelet@enscp.fr
Dedicated to Professor Lutz Tietze on the occasion of his 65th birthday
Abstract
We have found that functionalized acetylenic acids may be cyclized under extremely mild conditions, at room temperature in the presence of AuCl catalyst and without the use of additives. The corresponding 5-exo-alkylidene-butyrolactones were isolated in high yields, and this process constitutes an easy and efficient route to highly valuable building blocks of natural products having biological interest.
Keywords: Gold, catalysis, cyclization, carboxylic acids, functionalized .-butyrolactones
Introduction
Recent years have witnessed tremendous growth in the number of gold-catalyzed highly selective chemical transformations.1 Gold was considered as an inert metal for a long time, and its ability to behave as a soft Lewis-acid has recently been recognized as a source of inspiration for organic chemists. Gold catalysts may activate unsaturated functionalities such as alkenes, allenes and alkynes, and therefore allow the creation of carbon-carbon and carbon-heteroatom bonds under extremely mild conditions.1 Thus the addition of various nucleophiles to alkynes offers a fascinating opportunity to build up several complex and/or cyclic molecules. Various internal nucleophiles such as alkenyl,2 sulfur-,3 oxygen-4 and nitrogen-5 containing functions have been used in this regard. As part of our ongoing studies on metal-catalyzed atomeconomical reactions,6 we have been interested in the use of gold for simple and highly efficient transformations. We have found that AuI catalyst promotes a highly efficient cycloisomerization of bis-homopropargylic diols under very mild conditions and in very short time. This process,
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