Effects of Solvent and Additives on the Rearrangement Pathway of the Seyferth Reaction

Article abstract of DOI:10.1021/jo00217a007

The Seyferth reagent has dual reactivity with electron-deficient alkenes. trans-1,2-Dichloroethene reacts both with the free carbene to give cyclopropane stereospecifically and with a complex between carbene and a second molecule of Seyferth reagent (homogeneous catalysis) to give a rearranged propene.The addition of other materials to the reaction mixture can have a profound effect on the ratio of the two pathways.Good ? donors such as p-xylene decrease the pathway to rearranged propene via the complexed carbene.Such materials thus serve as inhibitors to the process of homogeneous catalysis by forming a competing complex that does not go on to propene but instead reverts to free carbene.The existence of the inhibitor-carbene complex is supported by concentration studies.The presence of insoluble materials such as zinc chloride, on the other hand , serves to decrease the pathway that leads through free carbene to the cyclopropane.Free carbene may react with the surface of the additive and be removed as a reactive species.This latter process would have no effect on carbene previously complexed with the homogeneous catalyst, the Seyferth reagent , which could still proceed to rearranged propene.