Dedicated to the 50th anniversary of SYNTHESIS
Abstract
A (4+3)-cycloaddition combines a four-atom synthon and three-atom synthon to form
seven-membered rings. In the past decade, many improvements have been made to this
class of cycloaddition, including excellent diastereo- and enantioselectivities, both
intra- and intermolecularly. Through the strategic use of transition-metal catalysts,
acids, bases, and organocatalysts, it is possible to perform the cycloaddition on
a variety of substrates, generating novel seven-membered rings. With these advances,
(4+3)-cycloaddition has also been applied to the synthesis of biologically relevant
compounds and natural products. We exclude the cycloadditions of cyclic dienes such
as furan, pyrrole, cyclohexadiene or cyclopentadiene as Chiu, Harmata, Mascareñas
and others have recently published thorough reviews on that topic. We will however
discuss the recent additions (2009–2020) to the literature for the (4+3)-cycloadditions
involving other types of four-atom synthons.
1 Introduction
2 Rhodium
2.1 Cyclopropanation/Cope Rearrangement
2.2 C–H activation
3 Gold, Silver
4 Copper
5 Palladium, Platinum, Iridium
6 Dual-Activation
7 Conclusion
Key words
(4+3)-cycloaddition - annulation - transition-metal catalysis