Bicyclofulvene, I. Darstellung von Methylenbicyclo[2.2.1]heptadien und Methylenbicyclo[4.2.1]nonatrien

Abstract

Die Titelverbindungen 3 und 7 wurden dargestellt, da in ihnen die semicyclische Doppelbindung wegen einer bicyclofulvenartigen Wechselwirkung der drei x-Systeme polarisiert sein kann. Um eine derartige Polarittit zu bestimmen, wurden zum Verglcich eine Rcihe von Methylenbicyclo[2.2. Ilheptan-und Methylenbicyclo[4.2.l]nonan-Derivaten mit abnehmender Zahl von Doppelbindungen dargestellt. Bicyclofulvenes, I SyntaeSis of Metbyle~ebicycl~2.2.llbepCadiew a d Methylenebicycl~4.2.l)nw~MeaeThe title compounds 3 and 7 have been synthesized because their semicyclic double bond could be polarized by a bicyclofulvene type interaction of the three x-systems. In order to detect such polarization a series of methylenebicyclo[2.2.l]heptane and methylenebicyclo-I4.2. llnonane derivatives of lesser unsaturation have been prepared for comparison.Pentafulven besitzt wie der Aromat Benzol sechs x-Elektronen. Wegen der gekreuzten Anordnung einer Doppelbindung sind die Elektronen des Fulvens so polarisiert, daD dex Carbocyclus ein aromatisches x-Elektronensextett auszubilden trachtet. Eine umgekehrte Polarisierung w&e bei einem ebenen Heptafulven moglichl), in dem die Elektronen des Carbocyclus den Status des aromatischen Tropyliumions anstreben. D i m mehr als nur formale Beziehung nvischen Fulven und Aromat sollte auch noch gelten, wenn man zu homoaromatischen Systemenz) iibergeht: d. h. daB 1) P. Garratt und P. Vollhardt, Aromatizitlt, Kap. 6; G. Thieme Verlag, Stuttgart 1973. Jungste Untenuchungen zeigten, daD eine derartige Polarisierung wegen sterischer Spannung nicht zum

Darstellung und Röntgenstruktur‐Analyse von 1,2,3,4,4a,9,9a,10‐Octahydro‐ syn ‐17‐methyl‐9, 10[1′,2′]benzeno‐1,4‐methanoanthracen, einer gespannten alkylaromatischen Verbindung. Vergleich mit Kraftfeld‐Rechnungen

“…Die Verbindung 2 kristallisiert aus Methylenchlorid in der triklinen Raumgruppe P 1 rnit zwei Molekulen in der asyrnrnetrischenEinheit rnit den Gitterkonstantena = 8.271 ( 5 ) , b = 12.634 (6) Tab. 3 .…”

An examination of the 9-heterobicyclo[4.2.1]nona-2,4,7-trienes by carbon-13 nuclear magnetic resonance

“…Continuing our analysis of the data we now make note of the fact that the chief influence that nonbonded lone pair transfer is expected to exert on the heteroatomic bridge of a molecule such as 1 is to enhance its effective electronegativity. Translated into l3C NMR observables, this anticipated increase in heteroatom electronegativity should manifest itself primarily as an increase in the magnitude of the l3C-H coupling constant of the "bridgehead" position, C(l), i.e., the carbon center directly linked to the bridge.6 In fact, by following the change of this l3C NMR constant during the structural transition of the 9-heterononabicyclo[4.2.1] frame from saturated 4 to partially unsaturated 2, 3 and, finally to fully unsaturated 1, it becomes possible to gain knowledge about the mechanism of nonbonded interaction and draw inference about its dependence on the nature of the bridging unit. To begin with, one notes that the fully saturated 4 does manifest the expected dependence of J C( 1)-H on heteroatom electronegativity, the recorded / (4) differential between the two extreme cases, i.e., for X = NH and X = O, rising to an impressive 11 Hz.…”

“…In the present instance, one finds the models to possess significantly different l3C-H coupling constants, a drop of ca. 20 Hz being observed on passing from puckered-localized la (J = 157 Hz) to planar-delocalized 4 (J = 137 Hz).2 This rather dramatic reduction in the magnitude of J is best and perhaps uniquely reasoned in terms of the enhancement in the "p" character of the C-H carbon hybrid which the nine-membered frame must experience to accommodate the widening of the C-C-C angle (120°-*• 140°) attending the change from heavily buckled (la) to Z>9/,-flat (4). 5 Upon applying this line of reasoning to the heteronins one is gratified to witness a similar downward trend of /Ti¿(13C-H)6 on going from the "polyenic" to the "aromatic" members of the family.…”