Catalyst- and Additive-Free Annulation of Ynediones and (Iso)Quinoline N-Oxides: An Approach to Synthesis of Pyrrolo[2,1-a]Isoquinolines and Pyrrolo[1,2-a]Quinolines

Abstract

A simple and effective annulation of ynediones and (iso)quinoline N-oxides was developed to afford various functionalized pyrrolo[2,1-a]isoquinolines and pyrrolo[1,2-a]quinolines in moderate to excellent yields. This protocol underwent a tandem [3 + 2] cycloaddition/ring-opening/N-nucleophilic addition, which exhibited high regioselectivity, broad substrate tolerance, and atom economy under catalyst-, additive-free, and air conditions. Moreover, indolizine was also successfully prepared using pyridine N-oxide.

Stereoselective synthesis of fused-, spiro- and bridged heterocycles via cyclization of isoquinolinium salts: a recent update

“…In 2020, Yavari's group reported a facile regio-and diastereoselective method to access to richly functionalized pyrrolo[2,1-a]isoquinolinones 17 via 1,3-dipolar cycloaddition 23 Among the various screened solvents (such as MeCN, CH 2 Cl 2 , DCE, DMF, DMSO, etc. ), THF was found to be the most effective solvent for the transformation.…”

Recent Applications of Quinolinium Salts in the Synthesis of Annulated Heterocycles

“…Wang's group disclosed a catalyst-free annulation of quinoline N-oxides 128 and ynedione 133 leading to the formation of pyrrolo[1,2-a]quinolines 134. 75 Quinoline N-oxides bearing electron-donating groups (Me, OMe) as well as electron-poor groups (such as Cl, NO2, CO2Me) were well tolerated and reacted with 1,4-diphenylbut-3-yne-1,2-dione 133, delivering the target compounds in moderate to excellent yields (Scheme 37). The reaction proceeded through a sequential [3+2] cycloaddition, ring opening, followed by Nnucleophilic addition process.…”

Phosphine-Catalyzed Synthesis of 3-Allyl-4-pyrones by the Tandem Reaction of Diynones and Allylic Alcohols

“…However, the preparation of functionalized allyl-4-pyrones has large challenge under metal-free condition, possibly due to the lack of suitable substrates. Inspired by the reaction of ynones with allylic alcohols and our successful transitions of ynones, we envisioned that 3-allyl-4-pyrones may be easily prepared from diynones and allylic alcohols through a tandem cyclization reaction under metal-free condition (Scheme d). Herein, we first reported a simple and efficient synthesis of 3-allyl-4-pyrones from diynones and allylic alcohols with high regioselectivity, broad substrate tolerance, and atom economy under metal-free condition.…”