Electronickel-Catalyzed Stereoselective Synthesis of Butafulvenes

Area of Science:

• Organic Chemistry
• Catalysis
• Synthetic Methodology

Background:

• Highly strained frameworks are challenging to synthesize selectively.
• Butafulvenes, benzene isomers with cyclobutene cores, present unique synthetic hurdles.
• Existing methods struggle with E/Z selectivity for secondary propargylic substrates.

Purpose of the Study:

• To develop a highly selective electrochemical nickel-catalyzed strategy for butafulvene synthesis.
• To overcome the E/Z selectivity challenge in synthesizing butafulvenes from secondary propargylic substrates.
• To establish a sustainable platform for accessing strained antiaromatic π-systems.

Main Methods:

• Electrochemical nickel-catalyzed direct electroreductive coupling of propargylic esters.
• Utilizing earth-abundant nickel and electricity under mild conditions.
• Investigating reaction intermediates (allenyl-Ni, bisallenyl-Ni, bisallene, nickelacycle) via mechanistic studies and cyclic voltammetry.

Main Results:

• Achieved regio-, chemo-, and stereoselective synthesis of butafulvenes.
• Successfully addressed the E/Z selectivity challenge, yielding separable products.
• Demonstrated broad substrate scope, including functional groups like bromide, carboxylate, and silyl groups.
• Enabled late-stage functionalization of complex molecules.

Conclusions:

• The developed protocol provides a general and sustainable method for synthesizing strained butafulvenes.
• Highlights the power of electro-nickel catalysis in stereoselective molecular assembly.
• Offers a new platform for accessing strained antiaromatic π-systems.