Pathways for Concerted [2 + 2] Cycloaddition to Cumulenes.

A computational search has revealed concerted pathways for [2 + 2] cycloaddition of ethylene to all 10 of the cumulenes with the formula X═C═Y, where X, Y = C, N, O, and S. Four different concerted pathways have been found, three of them pseudopericyclic plus another based on sp-hybridized carbon. In the case of 2 of the 16 possible cycloadditions, a pair of novel three-membered ring intermediates has been discovered.

Cycloaddition Chemistry of Tetrafluorothiophene S,S-Dioxide.

Tetrafluorothiophene S,S-dioxide has been found to be a powerful and versatile cycloaddend that undergoes a wide range of reactions as a Diels-Alder diene, dienophile, and [2 + 2] addend. Because it dimerizes only slowly at high temperatures, a broad range of conditions are available for these transformations. Reactions with terminal alkynes yield products of both Diels-Alder and [2 + 2] cycloaddition.

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.

Tetrafluorothiophene S,S-dioxide: a perfluorinated building block.

Tetrafluorothiophene S,S-dioxide, a highly reactive diene and dienophile, has been synthesized. A new route to 3,4-difluoro- and tetrafluorothiophene has been realized, and the previously unknown 2,3,4-trifluorothiophene has been obtained. The reactivity of tetrafluorothiophene S-oxide has been compared with that of the S,S-dioxide.

Photochemistry of o-fluoranil.

Initial exploration of the photochemical behavior of o-fluoranil has revealed dimer formation, cycloaddition to alkenes, and hydrogen abstraction from hydrocarbons, aldehydes, and ethers.