Shifa Zhu

A General and Efficient Cobalt(II)-Based Catalytic System for Highly Stereoselective Cyclopropanation of Alkenes with α-Cyanodiazoacetates

[Co(P1)], the cobalt(II) complex of the D(2)-symmetric chiral porphyrin 3,5-Di(t)Bu-ChenPhyrin, is an effective catalyst for catalyzing asymmetric olefin cyclopropanation with the acceptor/acceptor-type diazo reagent α-cyanodiazoacetates. The [Co(P1)]-catalyzed reaction is versatile and suitable for both aromatic and aliphatic olefins with varied electronic properties, including electron-rich and -poor olefins. The Co(II)-based catalytic system can be operated in a one-time protocol under mild conditions, affording the desired cyclopropane products in high yields with both high diastereo- and enantioselectivity. The resulting enantiomerically enriched 1,1-cyclopropanenitrile esters provide convenient access to a number of densely functionalized chiral cyclopropane derivatives, including α-cyclopropyl-β-amino acids.

Cobalt-Catalyzed Asymmetric Cyclopropanation with Diazosulfones: Rigidification and Polarization of Ligand Chiral Environment via Hydrogen Bonding and Cyclization

A new D2-symmetric chiral porphyrin P6 (2,6-DiMeO-ZhuPhyrin) with enhanced chiral rigidity and polarity was designed and synthesized through incorporation of hydrogen bonding and cyclic structure. Its cobalt(II) complex [Co(P6)] is a highly active and selective catalyst for asymmetric cyclopropanation of alkenes with diazosulfones. The [Co(P6)]-based catalytic system is suitable for various aromatic olefins as well as electron-deficient olefins, including alpha,beta-unsaturated esters, ketones, and nitriles, forming the corresponding cyclopropyl sulfones under mild conditions in high yields and high selectivities. In most cases, both excellent diastereo- and enantioselectivities were achieved.

Enantioselective Cyclopropenation of Alkynes with Acceptor/Acceptor-Substituted Diazo Reagents via Co(II)-Based Metalloradical Catalysis

The cobalt(II) complex of a new D(2)-symmetric chiral porphyrin 3,5-diMes-ChenPhyrin, [Co(P2)], has been shown to be a highly effective chiral metalloradical catalyst for enantioselective cyclopropenation of alkynes with acceptor/acceptor-substituted diazo reagents, such as α-cyanodiazoacetamides and α-cyanodiazoacetates. The [Co(P2)]-mediated metalloradical cyclopropenation is suitable to a wide range of terminal aromatic and related conjugated alkynes with varied steric and electronic properties, providing the corresponding trisubstituted cyclopropenes in high yields with excellent enantiocontrol of the all-carbon quaternary stereogenic centers. In addition to mild reaction conditions, the Co(II)-based metalloradical catalysis for cyclopropenation features a high degree of functional group tolerance.

Silver-Catalyzed Difunctionalization of Terminal Alkynes: Highly Regio- and Stereoselective Synthesis of (Z)-β-Haloenol Acetates

A new silver-catalyzed highly regio- and stereoselective difunctionalization reaction of simple terminal alkynes was reported in which the (Z)-beta-haloenol acetate derivatives were formed efficiently. The resulting products were versatile intermediates in organic synthesis.

Cobalt(II)‐Catalyzed Asymmetric Olefin Cyclopropanation with α‐Ketodiazoacetates

Cyclopropanes are a unique class of structure elements found in a number of biologically important compounds and have been demonstrated for a wide range of fundamental and practical applications.[1] One particularly attractive strategy for enantioselective synthesis of chiral cyclopropanes is based on transition metal-catalyzed asymmetric olefin cyclopropanation with diazo reagents.[2] In principle, chiral cyclopropane derivatives with all substitution patterns may be accessible in enantioenriched form by asymmetric cyclopropanation due to the diverse availability of both alkenes and diazo reagents. Among different classes of diazo reagents with various combinations of α-substituents, many acceptor- and donor/acceptor-substituted diazo reagents have been successfully employed as effective carbene sources for metal-catalyzed asymmetric cyclopropanation.[2] In contrast, the capacity of catalytic asymmetric cyclopropanation has not been fully explored with acceptor/acceptor-substituted diazo reagents, which would afford synthetically useful cyclopropane compounds bearing geminal electron-withdrawing functionalities.[3,4] Although there have been some recent successes in this area,[5–9] several important types of acceptor/acceptor-substituted diazo reagents remain challenging for asymmetric olefin cyclopropanation.

NHC-AuCl/Selectfluor: A Highly Efficient Catalytic System for Carbene-Transfer Reactions

The combination of NHC-gold complex and Selectfluor has been found to be a highly efficient catalyst system for carbene-transfer reactions, with a turnover number (TON) up to 990000 and a turnover frequency (TOF) up to 82500 h(-1).

Iron-catalyzed benzannulation reactions of 2-alkylbenzaldehydes and alkynes leading to naphthalene derivatives.

An efficient and practical method for the synthesis of naphthalene derivatives via Fe(III)-catalyzed benzannulation of 2-(2-oxoethyl)-benzaldehydes and alkynes has been developed. The system holds the advantages of cheap catalysts, wide substrate scope, and mild reaction conditions.

Gold‐Catalyzed Reactions of Enynals/Enynones with Norbornenes: Generation and Trapping of Cyclic o‐Quinodimethanes (o‐QDMs)

o-Quinodimethane (o-QDM), a transient short-lived and highly reactive species, has attracted great curiosity from chemists over the past 40 years, both from theoretical and synthetic points of view. As cis-dienes, o-QDMs are much more reactive than the related classical dienes (such as butadiene and cyclopentadiene) in Diels–Alder reactions (DA) with olefins. They can be classified as two main types based on their structures: acyclic o-QDMs and cyclic o-QDMs (Scheme 1). During the past decades, the acyclic o-QDM

Bioinspired Intramolecular Diels–Alder Reaction: A Rapid Access to the Highly‐Strained Cyclopropane‐Fused Polycyclic Skeleton

A bioinsipred gold-catalyzed tandem Diels-Alder/Diels-Alder reaction of an enynal and a 1,3-diene, forming the highly-strained benzotricyclo[3.2.1.0(2,7) ]octane skeleton, was reported. In contrast, a Diels-Alder/Friedel-Crafts tandem reaction occurred instead when silver salts were used as the catalyst. Although both reactions experienced the similar Diels-Alder reaction of a pyrylium intermediate with a 1,3-diene, they have different reaction mechanisms. The former proceeded with a stepwise Diels-Alder reaction, while the latter one with a concerted one.

Silver-Catalyzed Reaction of Enynals with Alkenes: A Tandem 1,3-Dipolar Cycloaddition/Cyclopropanation

A silver-catalyzed reaction of enynals with alkenes to synthesize a series of polycyclic compounds has been developed. The reaction occurred smoothly using enynals with electron-deficient alkynes or terminal alkynes as substrates. The reaction was proposed to proceed through a tandem 1,3-dipolar cycloaddition/cyclopropanation process. The preliminary investigations of the asymmetric catalytic version revealed that the biphosphine ligand could be used as the potential efficient chiral ligand.