In organic chemistry, a group transfer reaction is a class of the pericyclic reaction where one or more groups of atoms is transferred from one molecule to another. Group transfer reactions can sometimes be difficult to identify when separate reactant molecules combine into a single product molecule (like in the ene reaction). Unlike other pericyclic reaction classes, group transfer reactions do not have a specific conversion of pi bonds into sigma bonds or vice versa, and tend to be less frequently encountered. Like all pericyclic reactions, group transfer reactions must obey the Woodward–Hoffmann rules. Group transfer reactions can be divided into two distinct subcategories: the ene reaction and the diimide reduction. Group transfer reactions have diverse applications in various fields, including protein adenylation, biocatalytic and chemoenzymatic approaches for chemical synthesis, and strengthening skim natural rubber latex.
Mechanism
A defining feature of the group transfer reaction is that it is a concerted reaction, in which a bond is broken and formed in one step. The concerted reaction occurs due to the orbital overlap between the alkene and the allylic enophile.
none|thumb|500x500px|Figure 1. The mechanism of the group transfer reaction is allowed by the orbital overlap of the HOMO of the ene and the LUMO of the enophile.
Sub-categories of Group Transfer Reactions
Ene Reaction
The ene reaction is one of the most common forms of group transfer reactions, where an allylic hydrogen is transferred to an alkene in a cyclic concerted mechanism. The ene reaction is further divided into subgroups including intramolecular ene, metallo-ene, and carbonyl ene reactions. The reverse reaction, commonly called the retro-ene reaction, can occur under high temperatures.
[[File:Reduction_diimide.png|none|thumb|368x368px|Figure 3. Generic mechanism of a reduction with diimide adapted from Mandal.