Using the reaction of furans with singlet oxygen as a means to rapidly access huge structural diversity in green & sustainable way.

Abstract Ph 3 PAuNTf 2 (≈1 mol‐%) catalyzes the selective cycloisomerization of substituted aryl propargyl ethers into H ‐chromenes in excellent yields. Benzofuran byproducts are formed only case electron‐deficient arenes, up to 7 % relative yield. The ‐catalyzed cyclization was applied as a key step concise synthesis naturally occurring benzopyrans seselin, xanthyletin, precocenes I and II, 8‐(3′,3′‐dimethylallyl)wenteria chromene, 2,2‐dimethyl‐8‐prenylchromene‐6‐propenoic acid.

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

Supported gold nanoparticles catalyze the semihydrogenation of alkynes to alkenes with ammonia borane or amine complexes in excellent yields and under mild conditions. Internal provide cis-alkenes, making this protocol an attractive alternative classical Lindlar's hydrogenation.

Gold nanoparticles supported on TiO(2) (~1%) catalyse in high yields the selective cycloisomerisation of aryl propargyl ethers into corresponding 2H-chromenes, under heterogeneous conditions. 2H,2'H-3,3'-Bichromenes resulting from a catalytic oxidative dimerization pathway are also formed as by-products.

The first example of Au-catalyzed hydrosilylation allenes is presented using recyclable gold nanoparticles as catalyst, without the requirement any external ligands or additives. hydrosilane addition takes place on more substituted double bond terminal in a highly regioselective manner. observed regioselectivity/reactivity modes are attributed to steric and electronic factors.

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

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

Gold nanoparticles supported on TiO(2) (0.1-1% mol) catalyze at room temperature and 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 hydrogen gas. For majority substrates, yields are exceptional (up 99%). The reaction proceeds temperature, tolerates a variety functional groups, can be performed in several solvents.

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

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

Under catalysis by commercially available supported Au nanoparticles on TiO2 (1 mol %), terminal allenes undergo diboration and silaboration exclusively the double bond, in high yields stereoselectivity. In silaboration, boron moiety (Bpin) is attached carbon silyl group sp-C, a regioselectivity pattern that unusual. No ligands or additives are required, while catalyst recyclable reusable. The selectivity rationalized terms of π-allyl type an η-1 complex intermediate with apparent allylic...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTGeminal selectivity of singlet oxygen ene reactions. The nonbonding large group effectMichael Orfanopoulos, Manolis Stratakis, and Yiannis ElemesCite this: J. Am. Chem. Soc. 1990, 112, 17, 6417–6419Publication Date (Print):August 1, 1990Publication History Published online1 May 2002Published inissue 1 August 1990https://pubs.acs.org/doi/10.1021/ja00173a051https://doi.org/10.1021/ja00173a051research-articleACS PublicationsRequest reuse...

Gold nanoparticles supported on TiO2 catalyze under mild conditions the activation of a series 1,2-disilanes towards hydrolysis and alcoholysis, with concomitant evolution H2 gas. For case tert-benzyl alcohols, main or only pathway is reduction to corresponding alkanes.

Au nanoparticles supported on TiO2 (1 mol %) catalyze the quantitative cycloisomerization of conjugated allenones into furans under very mild conditions. The reaction rate is accelerated by adding acetic acid equiv), but does not participate in protodeauration step as corresponding Au(III)-catalyzed transformation. process purely heterogeneous, allowing thus recycling and reuse catalyst effectively several runs.

Supported Au nanoparticles on TiO2 catalyze the hydration/6-endo cyclization of skipped diynones to γ-pyrones in aqueous dioxane, via triple bond activation. The isomeric 3(2H)-furanones which could be formed through a competing and often prevailing 5-exo pathway using homogeneous ionic Au(I) catalysts were not seen. reaction does proceed initial 1,3-transposition their corresponding conjugated 1,3-diynone isomers. If methylamine is added, N-methyl-4-pyridones are exclusively 69-79% yields...

Natural weapons against HIV, litseaverticillols A (2) and C, have been synthesized from sesquirosefuran (1) by a rapid efficient biomimetic total synthesis involving chemo- stereoselective singlet-oxygen-initiated tandem sequence (see scheme). Litseaverticillols D, F, G were readily litseaverticillol through regioselective 1O2 ene reaction. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2003/z52180_s.pdf or author. Please note:...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDo rotational barriers dictate the regioselectivity in ene reactions of singlet oxygen and triazolinedione with alkenes?Michael Orfanopoulos, Manolis Stratakis, Yiannis Elemes, Frank JensenCite this: J. Am. Chem. Soc. 1991, 113, 8, 3180–3181Publication Date (Print):April 1, 1991Publication History Published online1 May 2002Published inissue 1 April...

Mesoporous nanocomposite frameworks of chromium(III) oxide and 12-phosphomolybdic acid (PMA) compounds were prepared via a "nanocasting" method, using mesoporous silica SBA-15 as the template. Small-angle X-ray scattering, transmission electron microscopy, nitrogen physisorption characterizations indicate that these materials possess well-ordered hexagonal mesostructure with high content PMA clusters (up to 63 wt %) large internal surface area 165 m2 g–1). The Keggin are incorporated intact...

In the presence of Au/TiO2 (1 mol %), terminal alkynes react quantitatively with stoichiometric amounts unactivated digermane Me3Ge-GeMe3, forming exclusively cis-1,2-digermylated alkenes. We also establish Au/TiO2-catalyzed hydrogermylation allenes Et3GeH, which exhibits a highly regioselective mode addition on more substituted double bond vinylgermanes. Additionally, we provide preliminary results regarding Pd nanoparticle-catalyzed C–C coupling 1,2-digermyl alkenes aryl iodides.