Recent Advances in Transition-Metal-Free (4+3)-Annulations

Abstract

(4+3)-Annulations are incredibly versatile reactions which combine a 4-atom synthon and a 3-atom synthon to form both 7-membered carbocycles as well as heterocycles. We have previously reviewed transition-metal-catalyzed (4+3)-annulations. In this review, we will cover examples involving bases, NHCs, phosphines, Lewis and Br nsted acids as well as some rare examples of boronic acid catalysis and photocatalysis. In analogy to our previous review, we exclude annulations involving cyclic dienes like furan, pyrrole, cyclohexadiene or cyclopentadiene, as Chiu, Harmata, Fern ndes and others have recently published reviews encompassing such substrates. We will however discuss the recent additions (2010 2020) to the literature on (4+3)-annulations involving other types of 4-atom-synthons. 1 Introduction 2 Bases 3 Annulations Using N-Heterocyclic Carbenes 3.1 N-Heterocyclic Carbenes (NHCs) 3.2 N-Heterocyclic Carbenes and Base Dual-Activation 4 Phosphines 5 Acids 5.1 Lewis Acids 5.2 Br nsted Acids 6 Boronic Acid Catalysis and Photocatalysis 7 Conclusion.