Cheletropic reaction

From Wikipedia, the free encyclopedia

A Cheletropic reaction is a pericyclic reaction where the net result is the conversion of a pi bond and a lone pair into a pair of sigma bonds; with both new sigma bonds adding into the same atom.

An example of such a reaction is the [1+4] reaction of sulfur dioxide with butadiene to form an adduct. The reverse of this process is often called Cheletropic extrusion, and is often performed, driven by the entropic benefit of gaseous evolution.

Another definition (from the IUPAC website)----

Cheletropic reaction A form of cycloaddition across the terminal atoms of a fully conjugated system with formation of two new s-bonds to a single atom of the (‘monocentric’) reagent. There is formal loss of one p-bond in the substrate and an increase in coordination number of the relevant atom of the reagent. An example is the addition of sulfur dioxide to butadiene: The reverse of this type of reaction is designated ‘cheletropic elimination’. 1994, 66, 1094 [IUPAC Compendium of Chemical Terminology 2nd Edition (1997)]