Cyclisation of biscarbenoids - a novel mode of cyclobutadiene stabilisation
Rüdiger Bertermann1, Holger Braunschweig1, Mehmet Ali Celik1
1Institut für Anorganische Chemie, Julius-Maximilians Universität Würzburg, Am Hubland, 97074 Würzburg, Germany. h.braunschweig@uni-wuerzburg.de.
Abstract:
The reaction of the vicinal biscarbenoid Pip-C[triple bond, length as m-dash]C-Pip with dimethyltin dichloride yields a unique tetraamino-substituted cyclobutadienyl system featuring a dative C-Sn interaction. DFT investigation of the reaction mechanism revealed that coordination of the stannyl fragment to the nucleophilic carbon leads to a metal-stabilised zwitterion, allowing for [2+2] cycloaddition under thermal conditions. The compound features a homoaromatic π-system comprising the three sp2-hybridised carbon atoms of the four-membered ring as a consequence of charge separation.
Related Concept Videos
Benzene to 1,4-Cyclohexadiene: Birch Reduction Mechanism
Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry
β-Dicarbonyl Compounds via Crossed Claisen Condensations
Cyclohexenones via Michael Addition and Aldol Condensation: The Robinson Annulation
Intramolecular Claisen Condensation of Dicarboxylic Esters: Dieckmann Cyclization
Preparation of Diols and Pinacol Rearrangement
The reaction begins with transferring a proton from the acid catalyst to one of the hydroxyl groups, producing an oxonium ion.


