Click chemistry beyond metal-catalyzed cycloaddition.
The overwhelming success of click chemistry encouraged researchers to develop alternative "spring-loaded" chemical reactions for use in different fields of chemistry. Initially, the copper(I)-catalyzed azide-alkyne cycloaddition was the only click reaction. In recent years, metal-free [3+2] cycloaddition reactions, Diels-Alder reactions, and thiol-alkene radical addition reactions have come to the fore as click reactions because of their simple synthetic procedures and high yields. Furthermore, these metal-free reactions have wide applicability and are physiologically compatible. These and other alternative click reactions expand the opportunities for synthesizing small organic compounds as well as tailor-made macromolecules and bioconjugates. This Minireview discusses the success and applicability of new, in particular metal-free, click reactions.
Becer
C Remzi
CR
Laboratory of Organic and Macromolecular Chemistry, Friedrich Schiller University Jena, Humboldtstrasse 10, 07743 Jena, Germany.
Hoogenboom
Richard
R
Schubert
Ulrich S
US