Recyclable catalytic synthesis of substituted quinolines: copper-catalyzed heterocyclization of 1-(2-aminoaryl)-2-yn-1-ols in ionic liquids

A convenient and simple approach for the recyclable catalytic synthesis of substituted quinolines is presented. The method is based on CuCl₂-catalyzed heterocyclization of readily available 1-(2-aminoaryl)-2-yn-1-ols in BmimBF₄ as the solvent at 100 °C for 15-24 h. The solvent-catalyst system could be successfully recycled up to six times without significant loss of activity.     

Diastereoselective formation of indanes from arylboronate esters catalyzed by rhodium(I) in aqueous media

[reaction: see text] Arylboronate esters bearing a pendant Michael-acceptor alkene can add to norbornene and cyclize to give indane systems in yields ranging from 62% to 95% with high diastereomeric excess (>20:1). The reaction is performed in an organic/aqueous emulsion and catalyzed using [Rh(COD)Cl]2 with t-Bu-amphos chloride, a sterically bulky, electron-rich, water-soluble phosphine ligand.     

A novel and efficient method for the Pd-catalysed oxidative carbonylation of amines to symmetrically and unsymmetrically substituted ureas

A new method for the Pd-catalysed oxidative carbonylation of amines to symmetrically and unsymmetrically substituted ureas with unprecedented catalytic efficiencies for this kind of reaction has been developed.     

Addition of bifunctional organoboron reagents to strained alkenes. Carbon-carbon bond formation with Rh(I) catalysis in aqueous media

Arylboronate esters bearing a pendant Michael-type acceptor olefin undergo transmetalation with a rhodium-based catalytic complex to generate a functionalized organorhodium intermediate that can cyclize onto strained olefins in good to excellent yields. The catalytic system involves the use of an electron-rich, sterically bulky ligand to stabilize the organorhodium intermediate and reduce the incidence of protodeboronation in aqueous media.     

Formation of homoallyl stannanes via palladium-catalyzed stannylative cyclization of enynes

[reaction: see text] Treatment of 1,6-enynes with tri(n-butyl)tin hydride in the presence of a catalytic amount of palladium acetate leads to the formation of exo-methylenecyclopentanes bearing a tri(n-butyl)stannylmethyl moiety.     

Rhamnogalacturonan II: Chemical Synthesis of a Substructure Including α-2,3-Linked Kdo**

The synthesis of a fully deprotected Kdo-containing rhamnogalacturonan II pentasaccharide is described. The strategy relies on the preparation of a suitably protected homogalacturonan tetrasaccharide backbone, through a post-glycosylation oxidation approach, and its stereoselective glycosylation with a Kdo fluoride donor.     

Use of Dithiasuccinoyl-Caged Amines Enables COS/H2S Release Lacking Electrophilic Byproducts

The enzymatic conversion of carbonyl sulfide (COS) to hydrogen sulfide (H₂S) by carbonic anhydrase has been used to develop self-immolating thiocarbamates as COS-based H₂S donors to further elucidate the impact of reactive sulfur species in biology. The high modularity of this approach has provided a library of COS-based H₂S donors that can be activated by specific stimuli. A common limitation, however, is that many such donors result in the formation of an electrophilic quinone methide byproduct during donor activation. As a mild alternative, we demonstrate here that dithiasuccinoyl groups can function as COS/H₂S donor motifs, and that these groups release two equivalents of COS/H₂S and uncage an amine payload under physiologically relevant conditions. Additionally, we demonstrate that COS/H₂S release from this donor motif can be altered by electronic modulation and alkyl substitution. These insights are further supported by DFT investigations, which reveal that aryl and alkyl thiocarbamates release COS with significantly different activation energies.