Cyclisch gekreuzt‐konjugierte Bindungssysteme, 37¹⁾Das vinyloge Sesquifulvalen

Abstract

Cyclic Cross-Conjugated Bond Systems, 37The Vinylogous Sesquifulvalene As a model study the tricycloheptenone 8 ("masked tropone") -obtained from quadricyclanone 7 -is used for the synthesis of the tricyclic fulvene 9, which upon Ago-catalysis or upon direct irradiation is quantitatively isomerized to the highly reactive sesquifulvalene 2. Applying the same scheme to the synthesis of the vinylogous sesquifulvalene 5, the tricyclic aldehyde 16 serves as precursor for the tricyclic fulvene 17, isomeric with 5. 17 is uniformly transformed into 5 in the presence of Ago. The isomeric fulvenes 25 and 26 are excluded as precursors of 5. Contrary to literature reports 5 is also obtained from 8-formylheptafulvene but only in very limited yield (max. 10%). 5 can be isolated in crystalline form and shows typical fulvalene-type spectral behavior.Irn Rahrnen des fruher skizzierten Programms zur Synthese der angular anellierten Perirnetermolekule C durch a,oElektrocyclisierung der vinylogen Fulvalene A (Fulvadiene)2) zu den Dihydro-Zwischenstufen B wurde zuerst die Zwolfelektronen-Elektrocyclisierung des vinylogen Pentafulvalens 4 (Pentafulvadien, A, rn = n = 2) verwirklicht j). Fur die erstaunliche Einheitlichkeit der Cyclisierung war entscheidend, daB 4 -wiewohl hochreaktiv -weniger zu intermolekularen Ausweichreaktionen neigt als das -wahrscheinlich starker verdrillte -, von Doering und Matzner beschriebene Grundgerust 1 (Pentaf~lvalen)~). Fur das vinyloge Sesquifulvalen 5 (Pentaheptafulvadien, A, m = 2, n = 3) konnte eine gegenuber 4 weiter verringerte Polyrnerisationsneigung erwartet werden. Diese fur die Reihe 1 -2 -34-' ) lange bekannte Tendenz setzt

Exploration of the π-Electronic Structure of Singlet, Triplet, and Quintet States of Fulvenes and Fulvalenes Using the Electron Localization Function

“…It can be noted that all compounds investigated herein, or derivatives thereof, have previously been synthesized, − and many of these compounds are found as ligands in organometallic complexes. − The results herein could thus have a direct impact on molecular design.…”

The Fulvalenes

“…[114] At about the same time Neuenschwander and his students [115,116] ob-tained 6 in 75-85 % yield from gas phase pyrolysis of 63 at 360°C and provided an analysis of the NMR spectroscopic data. [102] Shortly thereafter Prinzbach reported almost quantitative isomerisation of tricyclic fulvene 64 into 6 by Ag I catalysis (90 %) and upon photolysis (97 %), [117] while Hoffmann et al demonstrated that the norbornadiene 56d (R 1 = R 2 = R 3 = H) also gave 6 among a range of products from thermolysis at 500°C. [118] Much more recently, Li and Neuenschwander [119] have provided a potentially new general pathway to 6 (and heptafulvene and heptafulvalene 7) that currently terminates at 65 (Scheme 13).…”