# Chemo- and Regioselective Synthesis of 3,4-Dihydropyrimidin-4-ones from 4,5-Dihydro-1,2,4-oxadiazoles and Chromium Alkoxy Alkynyl Fischer Carbene Complexes

## TL;DR

A new method for making pyrimidin-4-ones using oxadiazoles and chromium complexes is developed, offering high selectivity and useful yields.

## Contribution

The first intermolecular use of 4,5-dihydro-1,2,4-oxadiazoles in forming six-membered heterocycles via a (3+3) cycloaddition.

## Key findings

- A formal (3+3) cycloaddition method for synthesizing pyrimidin-4-ones is achieved with high chemo- and regioselectivity.
- The reaction includes three diversity points and provides synthetically useful yields, including a gram-scale example.
- A proposed mechanism is supported by DFT calculations.

## Abstract

A completely chemo- and regioselective synthesis of pyrimidin-4­(3H)-ones by the reaction between 4,5-dihydro-1,2,4-oxadiazoles
and chromium alkoxy alkynyl Fischer carbene complexes is reported.
Overall, it is a formal (3+3) cycloaddition in which 4,5-dihydro-1,2,4-oxadiazoles
participate for the first time in the intermolecular formation of
six-membered heterocycles. Three points of diversity have been explored,
and usually, synthetically useful isolated yields are reached, including
one example at the gram scale. A reasonable mechanism, supported by
DFT calculations, is proposed.