The search for organic reactions proceeding with efficiency, selectivity and atom economy (i.e., all atoms of the reactants end up in the final product), has emerged as a major goal in synthetic chemistry.1 Isomerization reactions are typical examples of atom economic processes as no by products are generated. In this sense, the catalytic cycloisomerization of ?-alkynoic acids (1 ) promoted by transition-metals represents a straightforward route to synthetically useful cyclic enol-lactones (2 ). It is important to note that, in most of the cases, this catalytic transformation has only been carried out in organic solvents or in biphasic mixtures with water.2In this communication, we will present a simple and versatile iminophosphorane-Pd(II) complex 3  , as catalyst for the rapid, efficient and selective cycloisomerization of both terminal and internal ?-alkynoic acid (1 ) into their corresponding enol-lactones (2 ), which proceeds in water at room temperature and under air. In addition, the catalytic system could be also recycled in ten consecutive runs. Application of this methodology to the new tandem cycloisomerization/click chemistry reaction involving diynoic monoacids will be also discussed. (1) (a) Trost, B. M. Science 1991  , 254, 1471-1477. (b) Trost, B. M. Angew. Chem. Int. Ed. Eng. 1995  , 34, 259-281. (c) Trost, B. M.; Frederiksen, M. U.; Rudd, M. T. Angew. Chem. Int. Ed. 2005  , 44, 6630-6666.(2) (a) Mindt, T. L.; Schibli, R. J. Org. Chem. 2007  , 72, 10247. (b) Aleman, J.; del Solar, V.; Navarro-Ranninger, C. Chem. Commun. 2010  , 46, 454. (c) Aleman, J.; del Solar, V.; Mart�n-Santos, C.; Cubo, L.; Navarro-Ranninger, C. Eur. J. Org. Chem. 2011  , 76, 7287.

Pd(II)-catalyzed cycloisomerization of alkynoic acids in water: New tandem cycloisomerization/click chemistry reactions

244th National Meeting (2012)

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