Synthesis 2021; 53(22): 4134-4177
DOI: 10.1055/s-0040-1706023
special topic
Special Issue dedicated to Prof. Sarah Reisman, recipient of the 2019 Dr. Margaret Faul Women in Chemistry Award

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

Heather Lam
a   Davenport Research Laboratories, Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada
,
Xavier Abel-Snape
a   Davenport Research Laboratories, Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada
,
b   Ludwig-Maximilians-Universität München, Department Chemie und Biochemie, Butenandtstr. 5-13, 81377 München, Germany
,
Mark Lautens
a   Davenport Research Laboratories, Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada
› Author Affiliations
The authors would like to thank the Natural Sciences and Engineering Research Council (NSERC), Alphora Inc., and the University of Toronto for funding. H.L. thanks the NSERC Postgraduate Scholarships –Doctoral (PGS-D) program. X.A.-S. thanks the Ontario Graduate Scholarship (OGS) and the NSERC Canada Graduate Scholarships – Master’s (CGS-M) program. M.F.K. thanks the Deutscher Akademischer Austauschdienst (DAAD) (German Academic Exchange Service) and the Bayerischen Staat (State of Bavaria) for the PROSA LMU program.


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 Brønsted 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, Fernándes 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 Brønsted Acids

6 Boronic Acid Catalysis and Photocatalysis

7 Conclusion



Publication History

Received: 10 January 2021

Accepted after revision: 11 January 2021

Article published online:
23 February 2021

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