Axially Chiral Triazoloisoquinolin-3-ylidene Ligands in Gold(I)-Catalyzed Asymmetric Intermolecular (4 + 2) Cycloadditions of Allenamides and Dienes

The first highly enantioselective intermolecular (4 + 2) cycloaddition between allenes and dienes is reported. The reaction provides good yields of optically active cyclohexenes featuring diverse substitution patterns and up to three stereocenters. Key to the success of the process is the use of newly designed axially chiral N-heterocyclic carbene–gold catalystsThis work was supported by the Spanish MINECO (SAF2010-20822-C02, CTQ2010-15297, CTQ2010-14974, and Consolider Ingenio 2010 CSD2007-00006), the ERDF funds, the Xunta de Galicia (INCITE09209084PR, GRC2010/12), and the Junta de Andalucía (2008/FQM-3833 and 2009/FQM-4537, predoctoral fellowship to F.G.-C). H.F. acknowledges the Fundação para a Ciência e Tecnologia (FCT, Portugal) and POPH/FSE for a Ph.D. grant (Grant SFRH/BD/60214/2009)S

Metal-catalyzed intra- and intermolecular addition of carboxylic acids to alkynes in aqueous media: A review

The metal-catalyzed addition of carboxylic acids to alkynes is a very effective tool for the synthesis of carboxylate-functionalized olefinic compounds in an atom-economical manner. Thus, a large variety of synthetically useful lactones and enol-esters can be accessed through the intra- or intermolecular versions of this process. In order to reduce the environmental impact of these reactions, considerable efforts have been devoted in recent years to the development of catalytic systems able to operate in aqueous media, which represent a real challenge taking into account the tendency of alkynes to undergo hydration in the presence of transition metals. Despite this, different Pd, Pt, Au, Cu and Ru catalysts capable of promoting the intra- and intermolecular addition of carboxylic acids to alkynes in a selective manner in aqueous environments have appeared in the literature. In this review article, an overview of this chemistry is provided. The synthesis of β-oxo esters by catalytic addition of carboxylic acids to terminal propargylic alcohols in water is also discussed