# Pd/Ligand-Free Synthesis of 2-Alkynylated Pyrano[4,3-d]imidazol-4-ones via One-Pot Cu-Mediated Tandem Sonogashira Coupling/Regioselective 6-endo-dig Oxacyclization Reaction

## TL;DR

This paper presents a new efficient method to synthesize 2-alkynylated pyranoimidazol-4-ones using a one-pot copper-mediated reaction without palladium or ligands.

## Contribution

A novel palladium- and ligand-free one-pot tandem reaction for synthesizing 2-alkynylated pyranoimidazol-4-ones with high regioselectivity.

## Key findings

- The method achieves moderate to good yields of 2-alkynylated pyrano[4,3-d]imidazol-4-ones.
- The reaction shows broad compatibility with various terminal alkynes.
- DFT studies explain the regioselective 6-endo-dig oxacyclization mechanism.

## Abstract

Herein, we report a one-pot palladium- and ligand-free tandem Sonogashira coupling/regioselective 6-endo-dig oxacyclization reaction of 2,4-diiodo-1-methyl-imidazole-5-carboxylic acid with terminal alkynes mediated by Copper(I). This impressive approach offers a straightforward, practical, and efficient tandem procedure for accessing 2-alkynylated pyrano[4,3-d]imidazol-4-one in moderate to good yields with an exclusive 6-endo-dig oxacyclization. Notably, this cost-effective methodology demonstrates broad substrate compatibility with various commercially available aliphatic and (hetero)aromatic terminal alkynes. Furthermore, DFT studies were performed to elucidate the origin of this regioselective 6-endo-dig oxacyclization reaction.