Copper‐Catalyzed Group‐Transfer Radical Cyclization of γ,δ‐Unsaturated Oxime Esters: Synthesis of Ester‐Functionalized Pyrrolines

Enantioselective Borylcupration/Cyclization of Alkene-Tethered Oxime Esters

A copper-catalyzed enantioselective synthesis of borylated 1-pyrrolines from γ,δ-unsaturated oxime esters is reported. Twenty-four novel 1-pyrroline derivatives are reported in yields ranging from 26% to 96% and enantioselectivities from 74.5:25.5 er to 99:1 er. Examples derived from α-unsubstituted, non-fluorinated oxime esters are reported. The hydroxyl group following oxidation of the Bpin moiety acts as a directing group in highly diastereoselective reductions of the pyrrolines to the corresponding prolinol derivatives. Additionally, the Bpin group can be retained in the products following a simplified, chromatography-free workup procedure. DFT supports a reaction mechanism which proceeds through the formation of an (R)-benzylic copper intermediate, followed by stereoretentive cyclization with respect to the configuration at the metalated carbon. The conclusions of the computational data are corroborated through control experiments and deuterium-labelling studies.

Oxime Esters: Flexible Building Blocks for Heterocycle Formation

Oxime esters as the applicable building blocks, internal oxidizing agents, and directing groups in the synthesis of -, S-, and O-containing heterocycle scaffolds have gained great attention in the last decade. This review provides an overview of recent advances in the cyclization of oxime esters with various functional group reagents under transition metal and transition metal-free catalyzed conditions. Moreover, the mechanistic aspects of these protocols are explained in detail.

Recent Advances in Copper-Catalyzed C-N Bond Formation Involving N-Centered Radicals

C-N bonds are pervasive throughout organic-based materials, natural products, pharmaceutical compounds, and agricultural chemicals. Considering the widespread importance of C-N bonds, the development of greener and more convenient ways to form C-N bonds, especially in late-stage synthesis, has become one of the hottest research goals in synthetic chemistry. Copper-catalyzed radical reactions involving N-centered radicals have emerged as a sustainable and promising approach to build C-N bonds. As a chemically popular and diverse radical species, N-centered radicals have been used for all kinds of reactions for C-N bond formation by taking advantage of their inherently incredible reactive flexibility. Copper is also the most abundant and economic catalyst with the most relevant activity for facilitating the synthesis of valuable compounds. Therefore, the aim of the present Review was to illustrate recent and significant advances in C-N bond formation methods and to understand the unique advantages of copper catalysis in the generation of N-centered radicals since 2016. To provide an ease of understanding for the readers, this Review was organized based on the types of nitrogen sources (amines, amides, sulfonamides, oximes, hydrazones, azides, and tert-butyl nitrite).

Synthesis of Functionalized Pyrrolines via Microwave-Promoted Iminyl Radical Cyclizations

O-Phenyloximes tethered to alkenes undergo 5-exo-trig iminyl radical cyclizations upon microwave irradiation. Trapping of the resulting cyclic radicals results in C-C, C-N, C-O, C-S, or C-X bond formation. Allylic sulfides undergo a tandem cyclization-thiyl radical β-elimination, affording terminal alkenes. The cyclizations exhibit a broad scope, and in some cases they are highly diastereoselective. The pyrroline adducts are versatile intermediates that can be transformed into a range of different species.

Copper-catalyzed borylative cyclization of γ,δ-unsaturated aromatic oxime esters to (borylmethyl)pyrrolidines

An efficient copper-catalyzed aminoborylation of γ,δ-unsaturated aromatic oxime esters with bis(pinacolato)diboron has been developed. A variety of α-(borylmethyl)pyrrolidine derivatives were constructed in high yields under mild conditions.

Iron-catalyzed carbonylative cyclization of γ,δ-unsaturated aromatic oxime esters with amines

An efficient iron-catalyzed carbonylative cyclization of γ,δ-unsaturated aromatic oxime esters with amines has been developed.

Copper-catalyzed carbonylative synthesis of pyrrolidine-containing amides from γ,δ-unsaturated aromatic oxime esters

A new method of low-cost copper-catalyzed carbonylative cyclization for preparing pyrrolidine-containing amides from γ,δ-unsaturated aromatic oxime esters and amines has been described.

Recent advances in cyclization reactions of unsaturated oxime esters (ethers): synthesis of versatile functionalized nitrogen-containing scaffolds

We summarized recent advances in cyclization reactions of unsaturated oxime esters (ethers), which provide diversiform functionalized nitrogen-containing scaffolds.

Palladium-catalyzed cascade reactions of alkene-tethered carbamoyl chlorides with N-tosyl hydrazones: synthesis of alkene-functionalized oxindoles

An efficient approach for the construction of alkene-functionalized oxindoles was developed via palladium-catalyzed cascade reactions of alkene-tethered carbamoyl chlorides with N-tosyl hydrazones.

Silver-promoted cascade radical cyclization of γ,δ-unsaturated oxime esters with P(O)H compounds: synthesis of phosphorylated pyrrolines

We report the first silver-promoted imino-phosphorylation of γ,δ-unsaturated oxime esters with P(O)H compounds to synthesize various phosphorylated pyrrolines.