Gold-catalyzed cyclizations of alkynol-based compounds: synthesis of natural products and derivatives

One-pot enantioselective construction of 3,4-dihydro-2H-1,4-oxazines over Ru/Au relay catalysis and its mechanistic serendipity

One-pot enantioselective construction of 3,4-dihydro-2H-1,4-oxazines have been developed through the transfer hydrogenation/cyclization enantio-relay process using Ru and Au bimetallic catalysts.

The Divergent Cascade Reactions of Arylalkynols with Homopropargylic Amines or Electron-Deficient Olefins: Access to the Spiro-Isobenzofuran- b-pyrroloquinolines or Bridged-Isobenzofuran Polycycles

Two divergent cascade reactions of arylalkynols with homopropargylic amines or electron-deficient olefins were developed to synthesize the spiro-isobenzofuran- b-pyrroloquinolines or bridged-isobenzofuran heterocycles in good yields, respectively. One reaction actually involved intramolecular 5- endo-dig hydroamination cyclization-protonation of homopropargylic amines to give cycloiminium ions and intramolecular 5- exo-dig hydroalkoxylation cyclization of arylalkynols to generate isobenzofuran with exocyclic double bond, followed by the nontypical Povarov-type reaction in the presence of PtCl₂/FeCl₃ cocatalysts. The other underwent intramolecular hydroalkoxylation cycloisomerization of alkynols with the subsequent normal [4 + 2] cycoaddition with dienophiles. Herein, the arylalkynols acted as both "masked" electron-rich olefins and "masked" electron-rich dienes.

TBAF catalyzed one-pot synthesis of allenyl-indoles

The site selective synthesis of functionalized indoles is presented under environmentally convenient tetrabutylammonium fluoride catalysis.

Gold catalysis in total synthesis – recent achievements

The most recent achievements of gold catalysed transformations applied in total synthesis of natural products are reviewed and analysed.

A new microwave-assisted thionation-heterocyclization process leading to benzo[c]thiophene-1(3H)-thione and 1H-isothiochromene-1-thione derivatives

The first example of a MW-assisted tandem thionation/S-cyclization process, leading to benzothiophenethione and isothiochromenethione derivatives, is reported.

Exotines A and B, Two Heterodimers of Isopentenyl-Substituted Indole and Coumarin Derivatives from Murraya exotica

Exotines A and B (1 and 2), two heterodimers of isopentenyl-substituted indole and coumarin derivatives linked through a new fused heptacyclic ring system, were isolated from the roots of Murraya exotica. Their structures were established by comprehensive NMR and MS spectroscopic data analysis, and the absolute configurations were determined by single-crystal X-ray crystallographic analysis and ECD calculations. Compounds 1 and 2 showed inhibition of nitric oxide production in lipopolysaccharide-induced BV-2 microglial cells with IC50 values of 9.2 and 39.9 μM, respectively.

Gold-catalyzed diastereoselective cycloisomerization of alkylidene-cyclopropane-bearing 1,6-diynes

An unprecedented gold-catalyzed diastereoselective cycloisomerization of 1,6-diynes bearing an alkylidene cyclopropane moiety has been developed. This methodology enables rapid access to a variety of 1,2-trimethylenenorbornanes, which are important building blocks in the preparations of abiotic and sesquiterpene core structures.

Gold-catalyzed enantioselective ring-expanding cycloisomerization of cyclopropylidene bearing 1,5-enynes

An enantioselective ring-expanding cycloisomerization of 1,5-enynes bearing a cyclopropylidene moiety has been developed. This methodology provides a new approach to bicyclo[4.2.0]octanes, a structural motif present in many biologically active natural products.

A copper(ii) perchlorate-promoted tandem reaction of internal alkynol and salicyl N-tosylhydrazone: direct access to isochromeno[3,4-b]chromene

A copper(ii) perchlorate-promoted tandem reaction of internal alkynol and salicyl N-tosylhydrazone provides a novel, concise method for constructing isochromeno[3,4-b]chromene in 35–94% yields.

Gold catalysis: regio- and stereoselective total synthesis of xyloketals D and G and the related natural product alboatrin

A new and efficient one-pot desilylation-gold-catalyzed cycloisomerization of alkynes containing a silyl-protected phenolic -OH and a free alcoholic -OH unit leads selectively to the formation of tetrahydrofuranobenzopyran ring system. This approach has been used for the regio- and stereoselective synthesis of xyloketal D, xyloketal G, and the related natural product alboatrin.