Functional‐Group Chemistry of Organolithium Compounds: Photochemical [2+2] Cycloaddition of Alkenyl‐Substituted Lithium Cyclopentadienides

Abstract

Li and light: Alkenyl‐substituted lithium cyclopentadienides, which are in equilibrium with the substituted lithocene anion structure 1, undergo a photochemical [2+2] cycloaddition to yield selectively the carbon–carbon coupling product 2. This is a rare case of organic functional‐group chemistry for a reactive organolithium compound.

Recent Advances in the Synthesis of Cyclobutanes by Olefin [2 + 2] Photocycloaddition Reactions

“… 170 A related behavior was observed for alkenyl-substituted lithium cyclopentadienides. 173 Even a ladderane structure could be generated by employing a bis(butadienylcyclopentadienyl)zirconium complex. 174 Iwama et al showed that intramolecular [2 + 2] photocycloaddition reactions are possible between two double bonds in bridged bis(azulenyl) zirconocenes.…”

“…The Erker group employed this concept for the synthesis of novel ansa -metallocenes. − The bis­(2-alkenylindenyl)zirconium complex 69 for example gave upon direct excitation the cyclobutylene-bridged zirconocene 70 in a yield of 50% (Scheme ). A related behavior was observed for alkenyl-substituted lithium cyclopentadienides . Even a ladderane structure could be generated by employing a bis­(butadienylcyclopentadienyl)zirconium complex .…”

Electron-Transfer-Induced Intermolecular [2 + 2] Cycloaddition Reactions Based on the Aromatic “Redox Tag” Strategy

“…Furthermore, cycloreversion reactions have also been widely investigated because of their practical and theoretical potentials . In particular, electron-transfer-induced [2 + 2] cycloaddition reactions have extensively been studied . In order to generate radical ion intermediates, photochemical processes are widely employed .…”

Synthesis, Structural Characterization, and Reactivity of a Fluorene-Based Calcium Oxycyclopentadienide Complex

“…One calcium atom (Ca1) is attached to the Cp ring of a fluorene skeleton. The distances between Ca1 and carbon atoms in the Cp ring have a narrow range from 2.738(3) to 2.776(3) Å, indicating an η 5 mode interaction . Ca1 also coordinates with an exocyclic oxygen atom (O1) of another fluorene skeleton.…”