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

Abstract

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.

Pyridinium Ylide-Mediated Diastereoselective Synthesis of Spirocyclopropanyl-pyrazolones via Cascade Michael/Substitution Reaction

“…Over the years, the use of pyridinium ylides (PYs) has developed into an intriguing area of interest for scientists. Despite the stability and selectivity challenges associated with PY, many efficient methods have been developed to utilize PY. − Most of the reported methods on PYs display the formation of an indolizine type of molecule via 1,3-dipolar cycloaddition reaction. − Several reports on utilizing pyridinium ylides as C1 synthons for making C–C or C–X bonds to construct a wide range of cyclic systems have been reported. − …”

“…Based on the existing literature − and our previous research, , we hypothesized that arylidene/alkylidine-pyrazolones might serve as interesting C2/C4 synthons. These compounds could undergo Michael addition with the C1 synthon ammonium ylide followed by intramolecular substitution, resulting in the formation of spirocyclic or bicyclic privileged scaffolds (Figure ).…”