Enantioselective Cyclopropanation of a Wide Variety of Olefins Catalyzed by Ru(II)–Pheox Complexes

Abstract

The transition-metal-catalyzed asymmetric cyclopropanation of olefins with diazoacetates has become one of the most important methods for the synthesis of optically active cyclopropane derivatives, which are key pharmaceutical building blocks and present in a large number of natural products. To date, significant progress has been made in this area of research, and efficient stereocontrolled synthetic approaches to cyclopropane derivatives have been developed using rhodium, ruthenium, copper, and cobalt catalysts. However, the vast majority of these strategies are limited to electron-rich olefins, such as styrene derivatives, due to the electrophilicity of the metal-carbene intermediates generated from the reaction of the metal with the diazo compound. Recently, the D-symmetric Co(II)-phophyrin complexes developed by Zhang et al. were shown to be the most efficient catalysts for the asymmetric cyclopropanation of electron-deficient olefins. This catalytic system is mechanistically distinct from the previous rhodium and copper catalytic systems, proceeding via radical intermediates. However, the asymmetric cyclopropanation of vinyl carbamates, allenes, and α,β-unsaturated carbonyl compounds has rarely been reported. Therefore, the development of new powerful catalysts for the asymmetric cyclopropanation of a wide range of olefinic substrates is the next challenge in this field. In this Account, we summarize our recent studies on the Ru(II)-Pheox-catalyzed asymmetric cyclopropanation of various olefins, including vinyl carbamates, allenes, and α,β-unsaturated carbonyl compounds. We demonstrate that the developed catalytic system effectively promotes the asymmetric cyclopropanation of a wide variety of olefins to produce the desired cyclopropane products in high yields with excellent stereocontrol. The use of succinimidyl-, ketone-, and ester-functionalized diazoacetates as carbene sources was found to be crucial for the high stereoselectivity of the cyclopropanation reactions. In addition, we describe reusable chiral Ru(II)-Pheox catalysts, namely, water-soluble Ru(II)-hm-Pheox and polymer-supported PS-Ru(II)-Pheox, which can be reused at least five times in inter- and intramolecular cyclopropanation reactions without any significant loss of catalytic activity or enantioselectivity. These Ru(II)-Pheox-catalyzed asymmetric cyclopropanation reactions provide an elegant method to access a series of optically active cyclopropane derivatives, including cyclopropylamines, dicarbonyl cyclopropanes, alkylidenecyclopropanes, and cyclopropane-fused γ-lactones, which are intermediates in the syntheses of various biologically active compounds. The novel chiral Ru(II)-Pheox complexes are readily synthesized in high yield from inexpensive, commercially available benzoyl chloride and amino alcohols, then fully characterized using X-ray diffraction analysis, NMR, and elemental analysis. These catalysts are easy to handle and stable under ordinary temperatures and conditions and can be used after three months of storage without any...

Computational chemical analysis of Ru(II)‐Pheox–catalyzed highly enantioselective intramolecular cyclopropanation reactions

“…In 2010, we developed a novel chiral complex, Ru(II)‐phenyloxazoline (Ru(II)‐Pheox) complex, which has a unique C 1 ‐symmetric structure (Figure ). Ru(II)‐Pheox can be easily synthesized from a commercially available benzoic acid derivative, an amino alcohol and a Ru source, and effectively promotes enantioselective intermolecular and intramolecular cyclopropanations with electron‐rich olefins, as well as electron‐deficient olefins, under mild reaction conditions.…”

Diastereoselective Synthesis of Spirocyclopropanes under Mild Conditions via Formal [2 + 1] Cycloadditions Using 2,3-Dioxo-4-benzylidene-pyrrolidines

“…For instance, the ring-enlargement reactions of cyclopropanes with nucleophiles, such as amines, alcohols, and carboxylic acids, are efficient pathways to various heterocycles [ 21 , 22 , 23 , 24 , 25 , 26 , 27 ]. Consequently, numerous efforts have been devoted to the formation of three-membered carbocyclic rings during the last few decades [ 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ]. The reactions of carbenoids with alkenes such as the Simmons–Smith cyclo-propanation involving organozinc carbenes [ 37 , 38 , 39 , 40 ], or the addition of carbenes, generated from diazo compounds in the presence of transition metals, to double bonds [ 41 , 42 , 43 , 44 ] are the most significant and useful classical methods for the construction of cyclopropanes.…”

Rh(II)-mediated domino [4 + 1]-annulation of α-cyanothioacetamides using diazoesters: A new entry for the synthesis of multisubstituted thiophenes

“…In recent years the diversified reactivity of metal carbenes, catalytically generated from diazocarbonyl compounds, has found wide application in organic synthesis [ 1 – 16 ]. A particular interest was attracted recently to domino reactions of diazo compounds with intermediate formation of ylides [ 7 – 21 ].…”