RESUMO
A set of heterogenized olefin-metathesis catalysts, which consisted of Ru complexes with the H(2)ITap ligand (1,3-bis(2',6'-dimethyl-4'dimethyl aminophenyl)-4,5-dihydroimidazol-2-ylidene) that had been adsorbed onto a silica support, has been prepared. These complexes showed strong binding to the solid support without the need for tethering groups on the complex or functionalized silica. The catalysts were tested in the ring-opening-ring-closing-metathesis (RO-RCM) of cyclooctene (COE) and the self-metathesis of methyl oleate under continuous-flow conditions. The best complexes showed a TON>4000, which surpasses the previously reported materials that were either based on the Grubbs-Hoveyda II complex on silica or on the classical heterogeneous Re(2)O(7)/B(2)O(3) catalyst.
RESUMO
A general synthetic access to 3,3-disubstituted 1,4-diynes bearing a quaternary carbon center from acetylacetone was developed. The compounds were cyclized to the corresponding enol ethers by cationic gold complexes. The reactions occur in complete exo-selectivity in contrast to compounds incorporating an alkoxy substituent in the 3-position. A mechanistic rationale for this reversal of selectivity is provided.