Eine Cyanogruppe als Dienophil in einer intramolekularen π4 + π2-Cycloaddition

At elevated temperatures the 11, 14-cycloadducts of tetracyanoethylene with esters of retinoic acid or with retinol acetate are transformed into 5,9-methano-2H-cyclohepta[b]-pyridines by intermolecular _π4 + _π2-cycloaddition of a cyano group followed by a double bond shift. The resulting structure was determined by x-ray analysis.     

Inverse‐electron demand [π2 + σ2 + σ2] cycloaddition reaction of dimethyl oxaquadricyclane‐2,3‐dicarboxylate with cyclooctyne

A first example of an inverse‐electron demand [_π2 + _σ2 + _σ2] cycloaddition reaction of dimethyl oxaquadricyclane‐2,3‐dicarboxylate was reported: cyclooctyne underwent cycloaddition with dimethyl oxaquadricyclane‐2,3‐dicarboxylate to afford the corresponding adducts one of whose structure was confirmed by a single crystal X‐ray analysis.     

Nachweis von π → σ-Umlagerungen bei Ligandenverdrängungsreaktionen von π-Allyl-π-cyclopentadienyl-Palladiumkomplexen

It has been proved by NMR. measurements at low temperatures that the ligand displacement reactions of (π-all)Pd(π-C₅H₅) and Lewis bases L yielding PdL₄ proceed by a π → σ rearrangement of the allylic group as the primary step. The organic reaction product is the 1-isomer of the corresponding allylcyclopentadiene but in the reactions of (π-1,1,2-Me₃C₃H₂)Pd(π-C₅H₅) with L besides the isomeric allylcyclopentadienes also 2,3-dimethylbutadiene and cyclopentadiene are formed. The reaction mechanism will be discussed.