Chemoselective catalytic hydrodefluorination of trifluoromethylalkenes towards mono-/gem-di-fluoroalkenes under metal-free conditions

Jin-Dong Yang,Jin-Pei Cheng,Jingjing Zhang

doi:10.1038/s41467-021-23101-3

Abstract

Fluorine-containing moieties show significant effects in improving the properties of functional molecules. Consequently, efficient methods for installing them into target compounds are in great demand, especially those enabled by metal-free catalysis. Here we show a diazaphospholene-catalyzed hydrodefluorination of trifluoromethylalkenes to chemoselectively construct gem-difluoroalkenes and terminal monofluoroalkenes by simple adjustment of the reactant stoichiometry. This metal-free hydrodefluorination features mild reaction conditions, good group compatibility, and almost quantitative yields for both product types. Stoichiometric experiments indicated a stepwise mechanism: hydridic addition to fluoroalkenes and subsequent β-F elimination from hydrophosphination intermediates. Density functional theory calculations disclosed the origin of chemoselectivity, regioselectivity and stereoselectivity, suggesting an electron-donating effect of the alkene-terminal fluorine atom.

Highlights

Fluorine-containing moieties show significant effects in improving the properties of functional molecules
We described a method for metal-free catalytic activation of C–F bonds in trifluoromethylalkenes under mild conditions. gem-Difluoroalkenes and terminal monofluoroalkenes can be chemoselectively produced in almost quantitative yields by simple adjustment of the amount of the terminal reductant PhSiH3 (Fig. 2c)
A preliminary attempt indicated that the reaction of α-trifluoromethyl-styrene 2a with diazaphospholene 1 primarily gave the hydrophosphination intermediate A

Summary

Introduction

Fluorine-containing moieties show significant effects in improving the properties of functional molecules. Gem-Difluoroalkenes and terminal monofluoroalkenes can be chemoselectively produced in almost quantitative yields by simple adjustment of the amount of the terminal reductant PhSiH3 (Fig. 2c). When a second equivalent of diazaphospholene 1 was used, the in situ-generated gemdifluoroalkene 3a was further hydrodefluorinated at 70 °C to afford the dual-HDF product 4a in an almost quantitative yield after 1 h

Results

Conclusion