Biomedical subjects
Publications and source records attributed to David M Lemal.
[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.
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.
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.
The title compound, the first perhaloazulene, has been synthesized from hexachlorobutadiene and cyclopentadiene. Further chlorination of 1,3,4,5,6,7-hexachloroazulene results in addition, not substitution, under electrophilic as well as free radical conditions. Radical chlorination of the hexachloroazulene affords in good yield a single decachlorotetrahydroazulene. Treatment of this Cl(10) compound with one equiv of a phosphazene base gives a nonachlorodihydroazulene, but the addition of a second equiv results in dechlorination to 1,2,3,4,5,6,7-heptachloroazulene as well as dehydrochlorination to octachloroazulene. The former azulene is obtained cleanly from the Cl(9) compound with acid catalysis or by reduction with mercury. In the presence of calcium carbonate, however, the Cl(9) intermediate yields the dark green octachloroazulene. Although octachloronaphthalene is readily converted into its octafluoro counterpart, the isomeric octachloroazulene is far too sensitive to undergo the analogous transformation.