Soda Chanthamath

Highly Enantioselective Synthesis of Cyclopropylamine Derivatives via Ru(II)-Pheox-Catalyzed Direct Asymmetric Cyclopropanation of Vinylcarbamates

The Ru(II)-Pheox-catalyzed asymmetric cyclopropanation of vinylcarbamates with diazoesters resulted in the corresponding cyclopropylamine derivatives in high yield and excellent diastereoselectivity (up to 96:4) and enantioselectivity (up to 99% ee).

Highly Stereoselective Cyclopropanation of α,β‐Unsaturated Carbonyl Compounds with Methyl (Diazoacetoxy)acetate Catalyzed by a Chiral Ruthenium(II) Complex

Transition-metal-catalyzed asymmetric cyclopropanation of olefins with diazoacetates is a highly useful synthetic transformation for the construction of optically active cyclopropane frameworks, which are important structures because of their appearance in a wide variety of biologically active molecules. Therefore, during the past two decades, various catalytic systems have been developed for the highly diastereoand enantioselective cyclopropanation reactions. In particular, good stereocontrolled syntheses of cyclopropane derivatives have been achieved using copper, rhodium, ruthenium, and recently cobalt as catalysts. However, despite these considerable advances, only a few catalytic systems can catalyze the asymmetric cyclopropanation of electron-deficient olefins, such as a,b-unsaturated carbonyl compounds. Because of the electrophilic nature of the metal–carbene intermediate obtained by the reaction of metal complexes and diazoacetate, electron-rich olefins are generally preferred as reactants (Scheme 1).

Highly Stereoselective Synthesis of Cyclopropylphosphonates Catalyzed by Chiral Ru(II)-Pheox Complex

Ru(II)-Pheox-catalyzed asymmetric cyclopropanation of diethyl diazomethylphosphonate with alkenes, including α,β-unsaturated carbonyl compounds, afforded the corresponding optically active cyclopropylphosphonates in high yields and with excellent diastereoselectivity (up to 99:1) and enantioselectivity (up to 99% ee).

Ru(II)–Pheox-Catalyzed Asymmetric Intramolecular Cyclopropanation of Electron-Deficient Olefins

The first highly enantioselective intramolecular cyclopropanation of electron-deficient olefins, in the presence of Ru(II)--Pheox catalyst, is reported. The corresponding cyclopropane-fused γ-lactones were obtained in high yields (up to 99%) with excellent enantioselectivities (ee up to 99%). Moreover, this method enables efficient access to enantioenriched dicarbonyl cyclopropane derivatives, which are important intermediates for the synthesis of various bioactive compounds.

Highly Regio- and Stereoselective Synthesis of Alkylidenecyclopropanes via Ru(II)-Pheox Catalyzed Asymmetric Inter- and Intramolecular Cyclopropanation of Allenes

An efficient protocol for the synthesis of optically active alkylidenecyclopropanes (ACPs) via the Ru(II)-Pheox catalyzed asymmetric cyclopropanation of allenes has been established. This catalytic system proceeded with high regioselectivity to give the ACP products in high yield with high diastereoselectivity (up to 99/1) and enantioselectivity (up to 99% ee).

Direct Catalytic Asymmetric Cyclopropylphosphonation Reactions of N,N-Dialkyl Groups of Aniline Derivatives by Ru(II)-Pheox Complex

Novel catalysis involving phosphonomethylation of N-methylaniline and asymmetric cyclopropylphosphonation reactions of N,N-diethylaniline derivatives with diazomethylphosphonates are reported. Optically active cyclopropylphosphonate derivatives were directly synthesized from diazomethylphosphonates and N,N-diethylaniline derivatives catalyzed by a Ru(II)-Pheox complex in one step in good yields and high diastereoselectivities (up to trans/ cis = > 99:1<) and enantioselectivities (up to 99% ee). D-labeling mechanistic studies of phosphonomethylation and cyclopropylphosphonation suggested that an enamine or iminium intermediate was generated in the reaction process.

Ligand Exchange Reaction on a Ru(II)–Pheox Complex as a Mechanistic Study of Catalytic Reactions

A ligand exchange of one of the acetonitrile ligands of the (acetonitrile)4Ru(II)–phenyloxazoline complex (Ru(II)–Pheox) by pyridine was demonstrated, and the location of the exchange reaction was examined by density functional theory (DFT) calculations to study the mechanism of its catalytic asymmetric reactions. The acetonitrile was smoothly exchanged with a pyridine to afford the corresponding (pyridine)(acetonitrile)3Ru(II)–Pheox complex with a trans orientation (C–Ru–N(pyridine)) in a quantitative yield, and the complex was analyzed by single-crystal X-ray analysis. DFT calculations indicated that the most eliminable acetonitrile is the trans group, which is consistent with the X-ray analysis. The direction of the ligand exchange is thus determined on the basis of the energy gap of the ligand elimination instead of the stability of the metal complex. These results suggested that a reactant in a Ru–Pheox-catalyzed reaction should approach trans to the C–Ru bond to generate chirality on the Ru center.