Other Metal Catalysis Systems
Gold
The AuCl3-catalyzed double hydroalkoxylation of conjugated 7-hydroxyheptynoates offers a convenient route for the synthesis of six-membered cyclic acetals, which are common substructures of polyketide natural products [1]. When conjugated 6-hydroxyhexynoates are used as starting materials, either five-membered cyclic E-enol ethers or the corresponding acetals can be obtained by simply choosing the appropriate reaction solvent. NMR spectroscopic studies were carried out to determine the kinetics and pathway of the latterdomino 5-exocyclization-hydroalkoxylation reaction.
Iron
Catalytic FeCl3 in acetic acid has been employed as a cost-effective, low-toxicity reagent for the removal of butane 1,2-diacetal protecting groups under mild conditions [2].
Platinum
The synthesis of [4.2.1]- and [3.2.1]-fused bicyclic acetals by an intramolecular double alkoxylation of alkyne diols is reported [3]. The course of the reaction depends on the substitution of the triple bond. Terminal alkynes give the [3.2.1]bicyclic product by a 6-exopathway, whereas aryl alkynes undergo almost exclusively a 7-endo cyclization to give the [4.2.1]bicycles.
Metal Perovskites
The utility of perovskite-based materials in organic synthesis is explored through examination of a series of copper- and palladium-containing perovskites in Ullmann and Sonogashira type reactions [4]. La0.9Ce0.1Co0.6Cu0.4O3 is identified as an effective catalyst for the synthesis of a range of biaryl ether and thioether functionalities, whilst a Cu- and Pd-containing perovskite is effective in the Sonogashira reaction. These results suggest that perovskites may be useful leads in the search for new catalysts and reagents for organic synthesis.
Palladium-containing perovskites (LaFe0.57Co0.38Pd0.05O3) have been exploited as recoverable and reuseable catalysts in Suzuki coupling reactions; residual levels of Pd after removal of the catalyst by filtration are low (2 ppm) despite evidence that the reaction is occurring via a homogeneous process [5].
Iridium
A polymer-supported iridium catalyst has been prepared and used in the isomerisation of the double bonds in aryl allylic derivatives with excellent trans-selectivity and without the need for conventional work-up procedures [6].
Publications
1. AuCl3 catalysed hydroalkoxylation of conjugated alkynoates: synthesis of five and six-membered cyclic acetals A. Diéguez-Vázquez, C.C. Tzschucke, J. Crecente-Campo, S. McGrath, S.V. Ley Eur. J. Org. Chem. 2009, 40, 1698-1706
2. FeCl3 catalysed cleavage of 2,3-butanediacetal protected diols C.C. Tzschucke, N. Pradidphol, A. Dieguez-Vazquez, B. Kongkathip, N. Kongkathip, S.V. Ley Synlett 2008, 9, 1293-1296
3. PtCl4 catalysed domino synthesis of fused bicyclic acetals A. Diéguez-Vázquez, C.C. Tzschucke, Wing-Ye Lam, S.V. Ley Angew. Chem. Int. Ed. 2008, 47, 209-212
4. Copper- and palladium-containing perovskites: catalysts for the Ullmann and Sonogashira reactions S. Lohmann, S.P. Andrews, M.J. Burke, M.D. Smith, J.P. Attfield, H. Tanaka, K. Kaneko, S.V. Ley Synlett 2005, 1291-1295
5. Palladium-containing perovskites: recoverable and reusable catalysts for suzuki couplings M.D. Smith, C Ramarao, P.E. Brennan, A.F. Stepan, S.V. Ley
J. Chem. Soc., Chem. Commun. 2003, 2652-2653
6. A polymer-supported iridium catalyst for the stereoselective isomerisation of double bonds I.R. Baxendale, A-L Lee, S.V. Ley Synlett, 2002, 516-518
