concerted reaction

https://doi.org/10.1351/goldbook.CT07011
A single-step reaction through which reactants are directly transformed into products, i.e., without involvement of any intermediates.
Source:
PAC, 1999, 71, 1919. 'Glossary of terms used in theoretical organic chemistry' on page 1930 (https://doi.org/10.1351/pac199971101919)