Rh-Catalyzed Chemoselective [4 + 1] Cycloaddition Reaction toward Diverse 4-Methyleneprolines

Abstract

An efficient synthesis of 4-methyleneproline derivatives has been developed through an Rh-catalyzed [4 + 1] cycloaddition strategy using 3-methyleneazetidines and diazo compounds. The reaction proceeds under very mild conditions with a high degree of chemoselectivity, and competing experiments revealed that it is the preferred reaction, dominant over the C−H insertion, O−H insertion, and olefin cyclopropanation reactions which are commonly observed in Rh carbene chemistry. This method can incorporate the proline ester scaffold in pharmaceuticals and natural products. The intramolecular version of the reaction effectively provides proline-fused small to medium-sized tricyclic heterocycles. Gram-scale reactions, one-time addition of diazo compounds, and a minimum catalyst loading of 0.1 mol %, proceeded smoothly, implying their practicality.

Bifunctional 1-Boc-3-Iodoazetidine Enhancing Lithium Anode Stability and Rechargeability of Lithium–Oxygen Batteries

“…FTIR were performed to investigate the surface structure of the Li metal after immersing in BIA (Figure 1b). As shown in Figure 1b, compared with the pristine Li film, some new peaks at 1108, 1196, and 1614 cm −1 , which correspond to the C−N, C−O, and CO stretching vibrations, respectively, 26,27 can be observed for the Li metal after immersing in BIA. Furthermore, XPS was applied to analyze the surface compositions of Li metal after BIA treatment.…”

Rhodium‐Catalyzed One‐Carbon Ring Expansion of Aziridines with Vinyl‐N‐triftosylhydrazones for the Synthesis of 2‐Vinyl Azetidines

“…The pioneering works of multiple research groups have demonstrated the application of this approach for achieving 4-to 5-membered ring expansions through reacting with an azetidine with a diazo compound, leading to the formation of the corresponding pyrrolidine product (Figure 1A, left). [15][16][17][18][19] Considering the widespread usage of nitrogen heterocycles in various sectors of the chemical industry, particularly in the pharmaceutical field, the extension of this concept to other saturated N-heterocycles would be of immense value.…”

Rhodium‐Catalyzed One‐Carbon Ring Expansion of Aziridines with Vinyl‐N‐triftosylhydrazones for the Synthesis of 2‐Vinyl Azetidines

“…In the context of skeletal editing of saturated N ‐heterocycles via one‐carbon insertion, one potential mechanism for achieving ring expansion involves the sequential formation of an ammonium ylide and subsequent [1,2]‐stevens rearrangement, enabling efficient one‐carbon ring expansion. The pioneering works of multiple research groups have demonstrated the application of this approach for achieving 4‐ to 5‐membered ring expansions through reacting with an azetidine with a diazo compound, leading to the formation of the corresponding pyrrolidine product (Figure 1A, left) [15–19] . Considering the widespread usage of nitrogen heterocycles in various sectors of the chemical industry, particularly in the pharmaceutical field, the extension of this concept to other saturated N ‐heterocycles would be of immense value.…”

“…The pioneering works of multiple research groups have demonstrated the application of this approach for achieving 4-to 5-membered ring expansions through reacting with an azetidine with a diazo compound, leading to the formation of the corresponding pyrrolidine product (Figure 1A, left). [15][16][17][18][19] Considering the widespread usage of nitrogen heterocycles in various sectors of the chemical industry, particularly in the pharmaceutical field, the extension of this concept to other saturated N-heterocycles would be of immense value.…”