Biomedical subjects

Yigang He

Publications and source records attributed to Yigang He.

5 recordsLinked to original sources

PubMed2005

Opening of aryl-substituted epoxides to form quaternary stereogenic centers: synthesis of (-)-mesembrine.

[reaction: see text] Cycloalkanones are easily converted into aryl-substituted cyclic alkenes by the addition of an aryl Grignard reagent followed by dehydration. These alkenes are good substrates for asymmetric epoxidation. We have found that the addition of allylic and benzylic Grignard reagents can occur preferentially at the benzylic position of the derived epoxides to give the quaternary stereogenic center. This approach led to a short synthesis of the nanomolar serotonin re-uptake inhibitor (-)-mesembrine.

Indole Alkaloids↗

PubMed2004

Enantioselective construction of carbobicyclic scaffolds.

Allylic and benzylic Grignard reagents smoothly open phenylalkynyl-activated cyclic trisubstituted epoxides at the more substituted carbon atom to give secondary alcohols with a chiral quaternary center. These alcohols are good substrates for the construction of enantiomerically pure carbobicyclic scaffolds through intramolecular alkylation.

Bridged Bicyclo Compounds↗

PubMed2003

Diels-Alder reactions of perfluorobicyclo[2.2.0]hex-1(4)-ene with aromatics.

[reaction: see text] The title perfluoroalkene cycloadds to a variety of aromatic hydrocarbons, including benzene. It is the first alkene to yield a Diels-Alder adduct with benzene and is thus among the most potent dienophiles known.

Journal Article↗

PubMed2003

New syntheses and chemistry of hexafluorotropone.

Two new routes to hexafluorotropone have been developed, one from hexachlorotropone and a superior synthesis from hexafluorobenzene. Hexafluorotropone was found to be a very weak base, with a conjugate acid pK(a) of -6.2 +/- 0.5. The tropone adds in [6 + 4] fashion to cyclopentadiene and photocyclizes to hexafluorobicyclo[3.2.0]hepta-3,6-dien-2-one. Lithium hydroxide in benzene transforms the tropone into pentafluorotropolone, which functions as a bidentate ligand.

Journal Article↗

PubMed2003

A remarkable [2.2.2]propellane.

To explore the effects of fluorine substitution on the highly strained [2.2.2]propellane skeleton, a new representative of this ring system, perfluorotricyclo[2.2.2.01,4]octan-2-one ethylene ketal, was prepared by a rapid and quantitative [2+2] cycloaddition to the strained alkene perfluorobicyclo[2.2.0]hex-1(4)-ene. The propellane displays impressive thermal stability, and the vulnerable C-C bond joining the bridgeheads is very resistant to attack by electrophilic reagents. On the other hand, that electron-deficient bond is cleaved quickly at room temperature by a variety of nucleophiles and mild reducing agents. The behavior of this compound contrasts dramatically with that of the only known [2.2.2]propellane lacking fluorine substituents.

Journal Article↗