# Synthesis of Trifluoromethylated Spiroisoxazolones via a [3+2] Cycloaddition of Nitrile Imines and Unsaturated Isoxazolones

## TL;DR

This paper presents a new method to create trifluoromethylated spiroisoxazolones using a [3+2] cycloaddition reaction, which could be useful in drug development.

## Contribution

The first reported method to introduce a trifluoromethyl group at the 3-position of a pyrazoline ring via nitrile imine cycloaddition.

## Key findings

- The reaction yields spiroisoxazolones in moderate to high yields (up to 93%).
- The method shows broad compatibility with aromatic substituents on both reaction partners.
- The resulting compounds contain a CF3-substituted pyrazoline pharmacophore spiro-fused to an isoxazolone core.

## Abstract

A strategy for constructing trifluoromethylated spiroisoxazolones has been developed. This approach relies on the 1,3-dipolar cycloaddition of CF3-substituted nitrile imines, generated in situ from trifluoroacetyl hydrazonoyl bromides and K2CO3, with the exocyclic double bond of 4-benzylidene-3-methylisoxazol-5(4H)-ones. The reaction provides a series of trifluoromethylated spiro(isoxazolone-pyrazoline) derivatives in moderate to high yields (up to 93%). The protocol exhibits broad substrate compatibility with respect to aromatic substituents on both reaction partners. To the best of our knowledge, the introduction of a trifluoromethyl group at the 3-position of the pyrazoline ring via nitrile imine cycloaddition chemistry has not been previously reported. The resulting products incorporate a valuable CF3-substituted pyrazoline pharmacophore spiro-fused to an isoxazolone core and may be of interest for medicinal chemistry programs.