Recent Progress in Heterocycle Synthesis: Cyclization Reaction with Pyridinium and Quinolinium 1,4-Zwitterions

Heteroarene 1, n-zwitterions are powerful and versatile building blocks in the construction of heterocycles and have received increasing attention in recent years. In particular, pyridinium and quinolinium 1,4-zwitterions have been widely studied and used in a variety of cyclization reactions due to their air stability, ease of use, and high efficiency. Sulfur- and nitrogen-based pyridinium and quinolinium 1,4-zwitterions, types of emerging heteroatom-containing synthons, have attracted much attention from chemists. These 1,4-zwitterions, which contain multiple reaction sites, have been successfully used in the synthesis of three- to eight-membered cyclic compounds over the last decade. In this review, we present the exciting progress made in the field of cyclization reactions of sulfur- and nitrogen-based pyridinium and quinolinium 1,4-zwitterions. Moreover, the mechanistic insights, the transition states, some synthetic applications, and the challenges and opportunities are also discussed. We hope to provide an overview for synthetic chemists who are interested in the heterocycle synthesis from cyclization reaction with pyridinium and quinolinium 1,4-zwitterions pyridinium and quinolinium 1,4-zwitterions.

Recent Progress of Metal Nanoparticle Catalysts for C–C Bond Forming Reactions

Over the past few decades, the use of transition metal nanoparticles (NPs) in catalysis has attracted much attention and their use in C–C bond forming reactions constitutes one of their most important applications. A huge variety of metal NPs, which have showed high catalytic activity for C–C bond forming reactions, have been developed up to now. Many kinds of stabilizers, such as inorganic materials, magnetically recoverable materials, porous materials, organic–inorganic composites, carbon materials, polymers, and surfactants have been utilized to develop metal NPs catalysts. This review classified and outlined the categories of metal NPs by the type of support.

Stereoselective synthesis of spirocyclic pyrrolidines/pyrrolizidines/pyrrolothiazolidines using l-proline functionalized manganese ferrite nanorods as a novel heterogeneous catalyst

An efficient, green, one-pot, and three-component protocol has been reported for the stereoselective synthesis of a new class of spiro thiazolidines. A series of spiro-heterocycle derivatives were produced stereoselectively in high yields by the reaction of 5-arylidene thiazolidine-2,4-diones, isatin, and secondary amino acids in the presence of MnCoCuFe₂O₄@l-proline (MCCFe₂O₄@l-proline) magnetic nanorods as a novel nanocatalyst. The synthesized catalyst was fully characterized for thermal stability, magnetic properties, and other physicochemical properties via numerous techniques. It was applied as an efficient and reusable catalyst for the synthesis of endo-isomers of spirocyclic pyrrolidine/pyrrolizidine/pyrrolothiazolidine derivatives in high yield. The regioselectivity and stereochemistry of these heterocyclic spiro-compounds were established by ¹H, ¹³C, HMBC, HSQC, and COSY NMR spectroscopy techniques. The main attractive characteristics of the presented protocol are high yield, high level of diastereoselectivity, and easy recovery of catalyst without significant loss of its catalytic activity.

An efficient, green, one-pot, and three-component protocol has been reported for the stereoselective synthesis of a new class of spiro thiazolidines.