A form of
cycloaddition across the terminal atoms of a fully
conjugated system with formation of two new σ-bonds to a single atom of the ('
monocentric')
reagent. There is formal loss of one π-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'.
Source:
PAC, 1994, 66, 1077
(Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994))
on page 1094
