Manolis Stratakis

Selective isomerization of epoxides to allylic alcohols catalyzed by TiO2-supported gold nanoparticles.

ReacTiO(2)ns for rings: Gold nanoparticles supported on TiO(2) are used as a novel heterogeneous catalyst for the isomerization of epoxides to allylic alcohols by a concerted mechanism (see scheme). The reaction proceeds in high yields and the product selectivity is often remarkable.

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.

Oxidative cycloaddition of 1,1,3,3-tetramethyldisiloxane to alkynes catalyzed by supported gold nanoparticles.

Gold nanoparticles supported on TiO(2) (0.1-1% mol) catalyze at room temperature and at extremely mild conditions the unprecedented oxidative cycloaddition of 1,1,3,3-tetramethyldisiloxane to alkynes, forming substituted 2,5-dihydro-1,2,5-oxadisiloles, with concomitant evolution of hydrogen gas. For the majority of the substrates, the yields are exceptional (up to 99%). The reaction proceeds at room temperature, tolerates a variety of functional groups, and can be performed in several solvents.

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.

Regioselective reaction of singlet oxygen with cis-alkenes

Abstract The reaction of singlet oxygen with cis olefins is regioselective and shows a general preference for hydrogen abstraction on the larger alkyl group of the double bond.

Divergent synthesis of the co-isolated mycotoxins longianone, isopatulin, and (Z)-ascladiol via furan oxidation.

Longianone and the biosynthetically related mycotoxins isopatulin and (Z)-ascladiol were prepared following a divergent route from a readily available furan diol. The route toward longianone features an unprecedented TBAF-promoted intramolecular oxa-Michael reaction to a conjugated keto enoate, and the oxidation of dihydrolongianone to longianone with stabilized IBX. The route to isopatulin features a chemoenzymatic synthesis of (Z)-ascladiol, and the regioselective oxidation of (Z)-ascladiol to isopatulin with MnO(2).

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.

Solvent effects on the side selectivity of singlet oxygen with α,β unsaturated esters. New evidence for a perepoxide intermediate.

Abstract The side selectivity of the ene reaction of singlet oxygen with α, β-unsaturated esters depends on solvent polarity. These results are consonant with the formation of a perepoxide intermediate in the limiting step, of the title reaction.

Enhanced diastereoselectivity of an ene hydroperoxidation reaction by confinement within zeolite Na-Y; a stereoisotopic study

Abstract The ene reaction of singlet oxygen with the chiral alkene 2-methyl-5-phenyl-2-hexene in solution is not regioselective and exhibits very poor diastereoselectivity (∼10% d.e.). Within thionin-supported zeolite Na-Y, significant enhancement of product regioselectivity and diastereoselectivity (up to 54% d.e.) was obtained. Higher diastereoselectivity is found if the reaction occurs at the twix relative to the twin methyl group.

Reactions of triazolinediones with cis-alkenes. A highly regioselective ene reaction

Abstract The ene reaction of triazolinedione with unsymmetrical cis -alkenes is regiospecific and shows a preferential abstraction of the allylic hydrogens on the larger alkyl group of the double bond.