Ph 3 PAuNTf 2 (≈1 mol-%) catalyzes the selective cycloisomerization of substituted aryl propargyl ethers into 2H-chromenes in excellent yields. Benzofuran byproducts are formed only in the case of electron-deficient arenes, in up to 7 % relative yield. The Ph 3 PAuNTf 2 -catalyzed cyclization of

Gold nanoparticles supported on TiO(2) (1.2 mol %) catalyze, for the first time under heterogeneous conditions, the cycloisomerization of a series of 1,6-enynes in high yields. In several cases, the product selectivity differs significantly as compared to homogeneous Au(I)-catalysis. Based on product analysis and stereoisotopic studies it is proposed that the major or exclusive pathway involves a 5-exo cyclization mode to form stereoselectively gold cyclopropyl carbenes that undergo a single cleavage pathway, in contrast to homogeneous Au-catalysis where the double cleavage pathway operates substantially.

Supported gold nanoparticles on metal oxides (1 mol %) catalyze for the first time the cis-selective disilylation of terminal alkynes by 1,2-disilanes in isolated yields up to 94%. It is likely that the reaction proceeds through oxidative insertion of the σ Si-Si bond of disilanes on gold followed by 1,2-addition to the alkyne.

Gold nanoparticles supported on titania catalyse, even at a ppm loading level, the quantitative reduction of nitroarenes into anilines and nitroalkanes into alkylhydroxylamines by the ammonia· borane complex. No dehalohalogenation was seen in the case of chloro-or bromonitroarenes, while ester, cyano, or carboxylic acid functionalities also remain intact. The nitroarene to aniline reduction pathway does not require nitrosoarenes as intermediate products.

The first example of gold-catalyzed silaboration of alkynes with PhMe2SiBpin is documented in the presence of supported gold nanoparticles. In the case of terminal alkynes, the reaction proceeds at ambient conditions in very good yields and the regioselectivity is opposite to that observed in the presence of Pd or Pt catalysts. The abnormal regioselectivity is attributed to steric factors imposed by the Au nanoparticle during the 1,2-addition of silylborane to the alkyne.