Developing a transition-metal-free green protocol for the electrophilic hydrazination of silyl enol ethers using diazo electrophiles with EtOH–H2O as a safe solvent

Abstract

The scope of developing a green process for the electrophilic hydrazination of difluoro-substituted or desfluoro silyl enol ethers with diazo systems as electrophiles was examined. In contrast to conventional protocols that use a metal catalyst, a HF reagent, and chlorinated or ethereal solvents and are conducted at energy-inefficient low temperatures under an inert atmosphere, the new method allows reactions to be performed under metal- and HF-free conditions that take advantage of the eco-friendly, safer solvent system of EtOH–H₂O and exploit a more energy-efficient room temperature and an open air atmosphere. Additionally, the reaction protocol is amenable to multi-gram scale and suited to solvent-free conditions. The preparative scope of this operationally simple protocol was investigated in the context of thirty-eight examples to obtain synthetically important α-hydrazino ketone derivatives in good to excellent yields.