# Evolution of the Dearomative Functionalization of Activated Quinolines and Isoquinolines: Expansion of the Electrophile Scope

## TL;DR

This paper presents a new method for functionalizing quinolines and isoquinolines using a mild, metal-free or low-metal-catalyzed process with formic acid as a reductant.

## Contribution

The study introduces a transition-metal-free and low-catalyst protocol for dearomative functionalization with an expanded electrophile scope.

## Key findings

- The method enables the formation of substituted tetrahydro(iso)quinolines using diverse electrophiles.
- Electrophiles are incorporated at C-3 and C-4 positions, offering unique substitution patterns.
- The reactivity supports three annulation reactions to create complex polycyclic products.

## Abstract

Herein we disclose a mild protocol for the reductive functionalisation of quinolinium and isoquinolinium salts. The reaction proceeds under transition‐metal‐free conditions as well as under rhodium catalysis with very low catalyst loadings (0.01 mol %) and uses inexpensive formic acid as the terminal reductant. A wide range of electrophiles, including enones, imides, unsaturated esters and sulfones, β‐nitro styrenes and aldehydes are intercepted by the in situ formed enamine species forming a large variety of substituted tetrahydro(iso)quinolines. Electrophiles are incorporated at the C‐3 and C‐4 position for quinolines and isoquinolines respectively, providing access to substitution patterns which are not favoured in electrophilic or nucleophilic aromatic substitution. Finally, this reactivity was exploited to facilitate three types of annulation reactions, giving rise to complex polycyclic products of a formal [3+3] or [4+2] cycloaddition.