Intramolecular Cyclopropanation of Active Methylene Derivatives Based on FeCl2 or FeCl3-Promoted Radical-Polar Crossover Reactions

Radical-polar crossover reactions were studied for the intramolecular cyclopropanation of active methylene derivatives. In the presence of FeCl3 as a stoichiometric oxidant and K2HPO4 as a base, the dehydrogenative cyclopropanation of active methylenes proceeded through the FeCl3-promoted oxidative radical cyclization followed by the ionic cyclization to give the bicyclic cyclopropanes. The use of α-chloro-active methylenes leads the subcatalytic cyclopropanation involving two redox pathways. In the presence of K2HPO4, the redox cyclopropanation proceeded by using FeCl2 (20 mol%) in combination with ligand (20 mol%).

Low Coordination State RhI -Complex as High Performance Catalyst for Asymmetric Intramolecular Cyclopropanation: Construction of penta-Substituted Cyclopropanes

A simple, broad-scope rhodium(I)/chiral diene catalytic system for challenging asymmetric intramolecular cyclopropanation of various tri-substituted allylic diazoacetates was successfully developed. The low coordination state Rh^I -complex exhibits an extraordinarily high degree of tolerance to the variation in the extent of substitution of the allyl double bond, thus allowing the efficient construction of a wide range of penta-substituted, fused-ring cyclopropanes bearing three contiguous stereogenic centers, including two quaternary carbon stereocenters, in a highly enantioselective manner with ease at catalyst loading as low as 0.1 mol %. The stereoinduction mode of this Rh^I -carbene-directed asymmetric intramolecular cyclopropanation was investigated by DFT calculations, indicating that π-π stacking interactions between the aromatic rings of chiral diene ligand and diazo substrate play a key role in the control of the reaction enantioselectivity.

Concise synthesis and applications of enantiopure spirobiphenoxasilin-diol and its related chiral ligands

The development of chiral architectures for chiral ligand and catalyst discovery is essential for asymmetric catalysis. Herein, we report the concise synthesis of a Si-centered spirocyclic skeleton, spirobiphenoxasilin-diol (SPOSiOL), and its derived chiral ligands. Using the chemical resolution method, the optical SPOSiOL could be obtained in high yield on a gram scale. Preliminary studies indicated that this ligand scaffold has great potential in transition metal-catalyzed asymmetric reactions. This finding further highlights that the Si-centered spirocyclic scaffolds are of great value in asymmetric catalysis.

Synthesis of Forms of a Chiral Ruthenium Complex Containing a Ru-Colefin(sp2) Bond and Their Application to Catalytic Asymmetric Cyclopropanation Reactions

Organometallic complexes [Ru-C_olefin(sp²)-Ru(II)-Pheox 2a-2d] containing a Ru-C_olefin(sp²) bond have been prepared from unsaturated chiral oxazoline derivatives and evaluated for asymmetric cyclopropanation reactions. The corresponding optically active cyclopropanes were obtained with high yields and high stereoselectivities (≥99/<1 trans/cis, 99% trans ee). The enantioselectivities were found to be affected by the geminal substituent on the Ru-C(sp²) bond. In particular, Ru(II)-Prox catalyst 2c, in which there was no geminal substituent on the metal, was shown to have the highest enantioselectivities.

Iron catalysts with N-ligands for carbene transfer of diazo reagents

This review provides an overview of the catalytic activity of iron complexes of nitrogen ligands in driving carbene transfers towards CC, C–H and X–H bonds. The reactivity of diazo reagents is discussed as well as the proposed reaction mechanisms.

Rh(III)-Catalyzed Cyclopropanation of Unactivated Olefins Initiated by C-H Activation

We have developed a Rh(III)-catalyzed cyclopropanation of unactivated olefins initiated by an alkenyl C-H activation. A variety of 1,1-disubstituted olefins undergo efficient cyclopropanation with a slight excess of alkene stoichiometry. A series of mechanistic interrogations implicate a metal-carbene as an intermediate.