Gold-Catalyzed Formal [4+1]/[4+3] Cycloadditions of Diazo Esters with Triazines

Enantioselective [3+2] Cycloaddition of Donor-Acceptor Aziridines and Imines to Construct 2,5-trans-Imidazolidines

An enantioselective [3+2] cycloaddition of donor-acceptor aziridines with N-aryl protected imines was developed with a Ni(ClO₄ )₂  ⋅ 6H₂ O/N,N'-dioxide catalyst system, providing a broad range of chiral trans-substituted imidazolidine compounds with good yields and excellent enantioselectivities (up to 99 % yield, up to 98 % ee). Control experiments indicated that the products could offer excellent diastereoselectivities with the control of chiral Ni(II)-N,N'-dioxide complex and the interaction of the substrates. The possible catalytic process was proposed to rationalize the stereocontrol.

Non-globular organic ionic plastic crystal containing crown-ether moiety - Tuning its behaviour using sodium salts

Organic ionic plastic crystals (OIPCs) are a class of soft materials showing positional order while still allowing orientational freedom. Due to their motional freedom in the solid state, they possess plasticity, non‐flammability and high ionic conductivity. OIPC behavior is typically exhibited by ‘simple’ globular molecules allowing molecular rotation, whereas the interactions that govern the formation of OIPC phases in complex non‐globular molecules are less understood. To better understand these interactions, a new family of non‐globular OIPCs containing a 15‐crown‐5 ether moiety was synthetized and characterized. The 15C5BA molecule prepared does not exhibit the sought‐after behavior because of its non‐globular nature and strong intermolecular H‐bonds that restrict orientational motion. However, the OIPC behavior was successfully obtained through complexation of the crown‐ether moiety with sodium salts containing chaotropic anions. Those anions weaken the interactions between the molecules, allowing rotational freedom and tuning of the thermal and morphological properties of the OIPC.

Electrochemical formal [3 + 2] cycloaddition of azobenzenes with hexahydro-1,3,5-triazines

A catalyst-free electrochemical [3 + 2] cycloaddition of azobenzenes with hexahydro-1,3,5-triazines without an external oxidant has been developed for constructing the 1,2,4-triazolidine skeleton.

Synthesis of α-Amino Tertiary Alkylperoxides by Lewis Acid-Catalyzed Peroxidation of 1,3,5-Triazines

α-Substituted peroxides have been found in natural products and are widely used as anti-malarial agents. Zn(OTf)₂ -catalyzed peroxidation of 1,3,5-triazines has been developed, accessing diversely substituted α-amino tertiary alkylperoxides with high efficiency. Mechanistic investigations and useful synthetic application of the products have also been presented.

Transition-Metal-Catalyzed Cycloaddition Reactions to Access Seven-Membered Rings

The efficient and selective synthesis of functionalized seven-membered rings remains an important pursuit within synthetic organic chemistry, as this motif appears in numerous drug-like molecules and natural products. Use of cycloaddition reactions remains an attractive approach for their construction within the perspective of atom and step economy. Additionally, the ability to combine multiple components in a single reaction has the potential to allow for efficient combinatorial strategies of diversity-oriented synthesis. The inherent entropic penalty associated with achieving these transformations has impressively been overcome with development of catalysis, whereby the reaction components can be pre-organized through activation by transition-metal-catalysis. The fine-tuning of metal/ligand combinations as well as reaction conditions allows for achieving chemo-, regio-, diastereo- and enantioselectivity in these transformations. Herein, we discuss recent advances in transition-metal-catalyzed construction of seven-membered rings via combination of 2-4 components mediated by a variety of metals. An emphasis is placed on the mechanistic aspects of these transformations to both illustrate the state of the science and to highlight the unique application of novel processes of transition-metals in these transformations.

Gold-Catalyzed [3+2] Carbocycloaddition Reaction of Pinacol Alkenylboronates: Stereospecific Synthesis of Boryl-Functionalized Cyclopentene Derivatives

Gold-catalysis has enabled new synthetic opportunities in the chemistry of vinyldiazo compounds. Herein, we report the gold-catalyzed reaction of stabilized vinyldiazo compounds with pinacol alkenylboronates to provide boryl-functionalized cyclopentene derivatives through a formal [3+2] carbocycloaddition reaction, a very unusual pathway in alkenylboronate chemistry. This reaction proceeds with high regio- and stereoselectivity. The synthetic usefulness of the resulting borylated cyclopentene derivatives toward the synthesis of densely functionalized cyclopentanoids is also demonstrated.

Catalytic Divergent [3+3]- and [3+2]-Cycloaddition by Discrimination Between Diazo Compounds

Highly selective divergent cycloaddition reactions of enoldiazo compounds and α-diazocarboximides catalyzed by copper(I) or dirhodium(II) have been developed. With tetrakis(acetonitrile)copper(I) tetrafluoroborate as the catalyst epoxypyrrolo[1,2-a]azepine derivatives were prepared in good yields and excellent diastereoselectivities through the first reported [3+3]-cycloaddition of a carbonyl ylide. Use of Rh2 (pfb)4 or Rh2 (esp)2 directs the reactants to regioselective [3+2]-cycloaddition generating cyclopenta[2,3]pyrrolo[2,1-b]oxazoles with good yields and excellent diastereoselectivities.

A Stereoselective [3+1] Ring Expansion for the Synthesis of Highly Substituted Methylene Azetidines

The reaction of rhodium-bound carbenes with strained bicyclic methylene aziridines results in a formal [3+1] ring expansion to yield highly substituted methylene azetidines with excellent regio- and stereoselectivity. The reaction appears to proceed through an ylide-type mechanism, where the unique strain and structure of the methylene aziridine promotes a ring-opening/ring-closing cascade that efficiently transfers chirality from substrate to product. The resultant products can be elaborated into new azetidine scaffolds containing vicinal tertiary-quaternary and even quaternary-quaternary stereocenters.

Catalytic Asymmetric [3+1]-Cycloaddition Reaction of Ylides with Electrophilic Metallo-enolcarbene Intermediates

The first asymmetric [3+1]-cycloaddition was successfully achieved by copper(I) triflate/double-sidearmed bisoxazoline complex catalyzed reactions of β-triisopropylsilyl-substituted enoldiazo compounds with sulfur ylides. This methodology delivered a series of chiral cyclobutenes in good yields with high enantio- and diastereoselectivities (up to 99 % ee, and >20:1 d.r.). Additionally, the [3+1]-cycloaddition of catalytically generated metallo-enolcarbenes was successfully extended to reaction with a stable benzylidene dichlororuthenium complex.

Gold-Catalyzed Oxidative [2+2+1] Annulations of Aryldiazo Nitriles with Imines To Yield Polyarylated Imidazolium Salts

Gold-catalyzed oxidative [2+2+1] annulations between two imines and one α-cyano arylgold carbene afforded polyarylated imidazolium salts and molecular hydrogen efficiently. Control experiments suggest that the gold catalyst alone facilitates the main annulation, whereas Ag⁺ avoids the formation of inactive LAuCN. DFT calculations suggest that the success of this annulation relies on a 6 π-electrocyclization of cyano-free intermediates with cis-configured imines as initial reagents.

Highly Stereoselective Gold-Catalyzed Coupling of Diazo Reagents and Fluorinated Enol Silyl Ethers to Tetrasubstituted Alkenes

We report a highly stereoselective synthesis of all-carbon or fluorinated tetrasubstituted alkenes from diazo reagents and fluorinated enol silyl ethers, using C-F bond as a synthetic handle. Cationic Au^I catalysis plays a key role in this reaction. Remarkable fluorine effects on the reactivity and selectivity was also observed.