Asymmetric Catalytic Reactions of Donor–Acceptor Cyclopropanes

Abstract

Due to the synergistic “push–pull” effect of vicinal electron‐donating and electron‐withdrawing groups, donor–acceptor (D‐A) cyclopropanes have been recognized as one of the most powerful building blocks to generate polyfunctional reactive intermediates after a strain‐driven ring cleavage. Enantioselective reactions of D‐A cyclopropanes provide an efficient approach to enantioenriched acyclic and cyclic compounds. A number of chiral Lewis/Brønsted acids, transition metals, and organocatalysts have been designed for such transformations, including ring‐openings, annulations, and rearrangements. This minireview highlights the developments and new advances in this field and describes new synthetic opportunities offered by these interesting methodologies.

Ln(III)/Chiral Brønsted Acid Catalyzed Asymmetric Cascade Ring Opening/Aza-Piancatelli Rearrangement of D–A Cyclopropanes

“…Thus, discovery of a more efficient strategy for triggering the reaction and simultaneously realizing the enantioselective control is highly desirable. Lewis acids are known to facilitate the ring opening of donor–acceptor (D–A) cyclopropanes (CPs), − which was also successfully applied to initiate the aza-Pinacatelli reaction pioneered by Read de Alaniz’s group . However, the development of a catalytic asymmetric process has so far remained a challenge.…”

“…However, the development of a catalytic asymmetric process has so far remained a challenge. From a mechanistic viewpoint, unlike enantioselective nucleophilic ring-opening reactions of D–A CPs, − chiral information from the Lewis acid catalyst always coordinated at the 1,3-dicarbonyl position is relatively remote from the key 4π-pentadienyl cation intermediates involved in Piancatelli reaction. Our initial experiments indicated that employing chiral Lewis acid catalysis (with chiral Pybox or Box ligands) did not provide any enantioselective control (Table S1, see the Supporting Information).…”

Visible‐Light‐Mediated Ring‐Opening Reactions of Cyclopropanes

“…Due to the ring strain (approximately 28 kcal/mol), cyclopropanes are widely used as the precursor for the synthesis of various carbocycles, heterocycles, macromolecules and for other transformations by ring-opening reactions. [29][30][31][32][33][34][35][36][37][38] There exist various methods for the ring-opening transformations of cyclopropanes. [39][40][41][42][43][44][45] The pioneering ring-opening of cyclopropane was reported in 1966 by Schaafsma and co-workers.…”

Kinetic stabilization allows structural analysis of a benzoborirene

“…1–3 Deviations from ideal bonding arrangements result in an increased energy content compared to a hypothetical unstrained reference. The high energy content not only makes strained compounds highly reactive and thus valuable for chemical transformations, 4–11 but strain can also result in unusual structures that allow testing the limits of the theory of chemical bonding. Outstanding examples are the platonic hydrocarbons tetrahedrane and cubane that feature strongly distorted tetracoordinate carbon atoms.…”