Charis Gryparis

Cyclization of 1,6-enynes catalyzed by gold nanoparticles supported on TiO2: significant changes in selectivity and mechanism, as compared to homogeneous Au-catalysis.

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.

Nanogold-catalyzed cis-silaboration of alkynes with abnormal regioselectivity.

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.

Supported Gold Nanoparticle-Catalyzed cis-Selective Disilylation of Terminal Alkynes by σ Disilanes

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.

Biomimetic synthesis of dimeric metabolite acremine G via a highly regioselective and stereoselective Diels-Alder reaction.

The dimeric metabolite acremine G was synthesized featuring a highly regioselective and stereoselective Diels-Alder reaction between a TBS-protected hydroquinone diene and a structurally related alkenyl quinone. The major endo [4 + 2] adduct slowly transforms to acremine G by the atmospheric air under the deprotection conditions (in situ generated HF).