The Chemistry of Cyclopropanes and New Insights into Organocatalyzed Asymmetric Cyclopropanation

Cyclopropane structure has been the object of interest in multiple investigations due to its prevalence in different natural products. In addition, this structure has a particular reactivity, specifically the 1,1-cyclopropanedicarboxylate compounds, which act as acceptor-donor cyclopropanes. Its reactivity could be compared with that of an alpha,beta-unsaturated carbonyl, which undergoes conjugate addition reaction and depending on the nature of the nucleophile this can lead to a cycloaddition reaction. Therefore, cyclopropane can be transformed into several useful structures in organic synthesis. Different methods have been described to achieve cyclopropanes such as, Simmons-Smith reaction, decomposition of diazoalkanes and Michael-Initiated ring closure (MIRC). Due to the absence of metals, this last method has been applied to the asymmetric organocatalytic synthesis of cyclopropanes, where the substrates activation is through the imine-enamine intermediates formation or by hydrogen bonds. The asymmetric reaction consists of a domino reaction composed of a conjugate addition reaction and a cyclization reaction via intramolecular nucleophilic substitution. In this review, different asymmetric organocatalytic syntheses of the last two decades until 2021 are presented. With the intention to facilitate the reading of the review, an example of each paper was selected with the optimal reaction conditions and with the best organocatalyst producing the best yield and high stereoselectivity.