C-Ethynylpyrroles or -indoles, which can be prepared by cross-coupling of pyrroles or indoles with haloalkynes on active surfaces, undergo [2+2]-cycloaddition reactions with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone to give 2-pyrrolyl- or 3-indolylbicyclooctadienes in almost quantitative yields. The adducts are charge-transfer complexes that are paramagnetic in the solid state, and therefore represent a new family of densely functionalized pyrrole and indole derivatives potentially useful as pharmaceutical candidates, highly potent building blocks, or precursors of advanced materials. The reaction contributes to the practical and basic chemistry of pyrroles, indoles, alkynes, and quinones.
Rearrangements of the [2+2]-cycloadducts of DDQ and 2-ethynylpyrroles
作者:Boris A. Trofimov、Lyubov N. Sobenina、Zinaida V. Stepanova、Igor A. Ushakov、Albina I. Mikhaleva、Denis N. Tomilin、Olga N. Kazheva、Grigorii G. Alexandrov、Anatolii N. Chekhlov、Oleg A. Dyachenko
DOI:10.1016/j.tetlet.2010.07.100
日期:2010.9
2-ethynylpyrroles, upon ethanolysis (reflux, 15 min or room temperature, 24 h), rearrange frombicyclo[4.2.0]octadienediones to bicyclo[3.2.0]heptadienone- and cyclobutenyl-dihydrofuranone moieties in 55–83% yields, the former rearrangement being the major direction. Benzoquinone ring cleavage is regioselective to afford mostly bicyclo[3.2.0]heptadienone-pyrrole ensembles (85–90% selectivity) in 39–78% yields. The