Recent Applications of Quinolinium Salts in the Synthesis of Annulated Heterocycles

Abstract

AbstractQuinoline derivatives are frequently found in natural products and biologically active compounds; however, construction of quinoline fused polyheterocycles is a challenging goal in synthetic organic chemistry. In this regard, quinolinium salts meet the demand to a great level, as they can be synthesized readily and employed effectively for rapid construction of the condensed heterocyclic core. The present review focuses on recent (2015–2021) applications of different quinolinium salts, which react with suitable partners to access diverse annulated products. Most of the reactions discussed here involve easily available starting materials, are operationally simple, offer high atom-efficiency, and are environmentally benign. Mechanistic aspects of representative transformations have also been highlighted to better understand the reaction pathways.1 Introduction2 Annulation Involving N-Alkyl Quinolinium Salts2.1 Reaction with Alkenes2.2 Reaction with Alkynes/Arynes2.3 Reaction with Phenolic Compounds2.4 Reaction with Cyclic/Acyclic Diketones2.5 Reaction with Amines/Cyclic Amines2.6 Reaction with Enamines2.7 Reaction with Isocyanoacetates2.8 Reaction with Cyclopropanes2.9 Ring Expansion Reactions3 Annulation Involving Quinolinium Zwitterionic Tosylates3.1 Reaction with Alkynes/Arynes3.2 Reaction with Allenes/Ketenes3.3 Reaction with Aldehyde-Amino Acid (Azomethine Ylide)3.4 Reaction with Sulfonium Salts3.5 Reaction with Diazoacetate4 Annulation Involving Quinolinium Zwitterionic Thiolates4.1 Reaction with Sulfonium Salts4.2 Reaction with Sulfenes4.3 Reaction with Arynes5 Annulation Involving Quinoline N-Oxides5.1 Reaction with Diynes and Ynones5.2 Lactonization Involving Acrylate6 Annulation Involving N-Iminoquinolinium Salts6.1 Reaction with Allenoates6.2 Reaction with Hydroxymethylallyl Carbonate7 Miscellaneous Cyclizations8 Conclusions