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

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