title: The second cyclopropannulene: cycloprop-[8]annulene.
abstract: Reacting (at 0 degrees C) a mixture of CH2Cl2 and monobromo[8]annulene (C8H7Br) with potassium tert-butoxide in hexamethylphosphoramide (HMPA) and following with exposure to potassium metal led to the formation of the anion radical of an HMPA-[6.1.0]bicyclononatetraene condensation product, in which two HMPA fragments are geminal and attached to the number 9 carbon. When the reaction sequence is carried out in THF, the dianion of cycloprop[8]annulene is predominantly formed. Neutral cycloprop[8]annulene can be isolated via the I2 oxidation of the THF solution. The NMR analysis reveals that the eight-membered ring is nearly planar, and the three-membered ring is more like a dimethylenecyclopropane than it is like a cyclopropene. Further, the chemical shifts due to the protons on the eight-membered ring are nearly 2 ppm further upfield than are those for [8]annulene itself, suggesting a paratropic ring current.
authors.affiliation: Department of Chemistry, Illinois State University, Normal, Illinois 61790-4160, USA.
authors.forename: Matthew K
authors.initials: MK
authors.lastname: Kiesewetter
authors.forename: Richard C
authors.initials: RC
authors.lastname: Reiter
authors.forename: Cheryl D
authors.initials: CD
authors.lastname: Stevenson