David M. Lemal

Concerning the ‘Wanzlick equilibrium’

Abstract A negative crossover experiment performed in the 1960s which ruled out Wanzlicks tetraaminoethylene–diaminocarbene equilibrium gave erroneous results, according to a recent claim by Denk. In response, this system has been reinvestigated. When potassium hydride is present to preclude electrophilic catalysis, no crossing over occurs and starting tetraaminoethylenes are recovered unchanged. The original conclusion regarding the proposed equilibrium is thus reaffirmed.

Organic chemistry: aromatics do the twist.

For nearly 40 years, organic chemists have been fascinated by the idea of aromatic molecules that have the topology of a Möbius strip. No such molecule has been isolated — until now.

o-Fluoranil chemistry: Diels-Alder versus hetero-Diels-Alder cycloaddition.

The title quinone undergoes [4 + 2] cycloadditions in two ways, Diels-Alder on the ring and hetero-Diels-Alder by attack at the oxygens. The latter mode of reaction is strongly favored thermodynamically, but there is a kinetic bias favoring the normal Diels-Alder addition that often prevails, especially with cycloaddends that are not electron-rich.

The multifaceted reactivity of o-fluoranil.

In addition to Diels-Alder and hetero-Diels-Alder reactions, tetrafluoro-o-benzoquinone (o-fluoranil) undergoes nucleophilic additions, addition-eliminations, dioxole formation, and charge-transfer complexation, reacting at every site on the molecular skeleton. It also effects dehydrogenations and other oxidations. The quinone can function as a (CF)(4) synthon.

o-Fluoranil: stereochemistry and mechanism of its Diels-Alder reactions.

In the absence of significant steric effects, Diels-Alder reactions of the title quinone generally take place with preservation of configuration, and are therefore probably concerted. However, hybrid density functional calculations indicate that often these reactions are highly asynchronous. Steric hindrance can result in reaction at quinone oxygen instead of carbon. Preference for endo over exo cycloaddition is observed, and is reinforced by a repulsive secondary orbital interaction in exo transition states.

The Effect of Fluorine Substitution on Ring Inversion in Bicyclo[1.1.0]butanes

Degenerate ring inversion in bicyclo[1.1.0]butane and eight of its fluorinated derivatives has been studied at the B3LYP/6-311G**+ level of theory. Fluorine substitution lowers the inversion barrier impressively; reasons for this phenomenon are discussed.

Synthetic approaches to a fluorinated tetrahedrane

Abstract Approaches to tetrakis(2-chlorotetrafluoroethyl)tetrahedrane ( 2 ) from 1,6-dichlorooctafluoro-3-hexyne ( 4 ) have been explored. The synthesis and chemistry are described of cyclopropenyl ketenimines ( 6a , b ), a Dewar thiophene ( 24 ) and a cyclobutadienetricarbonyliron complex ( 33 ) derived from this acetylene.

Anesthetic properties of some fluorinated oxolanes and oxetanes.

BACKGROUND: The search for new potent inhaled anesthetics has slowed, in large part because of the excellence of the two most recent additions, desflurane and sevoflurane. Nonetheless, neither desflurane nor sevoflurane are ideal anesthetics, desflurane causing cardiorespiratory stimulation, and sevoflurane having a slower (albeit rapid) recovery from anesthesia. Sevoflurane also can produce convulsions and postoperative agitation. METHODS AND RESULTS: In the present report, we describe the physical and anesthetic properties of 31 cyclic ethers halogenated solely with fluorine. Although several produced anesthesia, none had solubilities that would make them better than sevoflurane. The remaining ethers were unstable or produced obvious central nervous system irritation, including convulsions. CONCLUSIONS: We find that none of these cyclic ethers appear to provide advantages over desflurane or sevoflurane.

FUNCTIONALIZATION OF SATURATED FLUOROCARBONS

Abstract A method is described for transforming perfluoroalkanes and perfluorocycloalkanes bearing tertiary fluorine into perfluoroenolates, which can be variously derivatized.

Synthesis and properties of the strained alkene perfluorobicyclo[2.2.0]hex-1(4)-ene.

The title fluoroalkene has been generated by dehalogenation of dibromide and diiodide precursors and trapped in situ. retro-Diels-Alder reaction of its adduct with N-benzylpyrrole has made the alkene available in high yield and purity. In sharp contrast to its extremely labile hydrocarbon counterpart, the fluoroalkene is very stable yet highly reactive. Its characterization includes its electron affinity, photoelectron spectrum, and the previously reported structure determination by electron diffraction.