Reductive anti-dimagnesiation and dialumination of alkynes: Synthesis and reactions of trans-1,2-dimetalloalkenes

Given the great significance of polar reactive organometallic species in synthesis for more than one century, generation and use of stereodefined 1,2-dimetallated alkenes should be fascinating yet has been very challenging. Here we report reductive anti-1,2-dimetalation of alkynes to easily and stereoselectively generate trans-1,2-dimagnesio- and 1,2-dialuminoalkenes that are difficult to prepare, reasonably stable, and thus useful for organic synthesis. The key for the success is the use of sodium dispersion as a powerful reducing agent and organomagnesium and organoaluminum halides as reduction-resistant electrophiles counterintuitively. Highly nucleophilic 1,2-dimagnesioalkenes serve as dual Grignard reagents and react with various electrophiles to afford anti-difunctionalized alkenes. Interestingly, 1,2-dialuminoalkenes react with paraformaldehyde with dearomatization of the aryl moieties to form the corresponding dearomatized 1,4-diols, the overall reaction being regarded as alkynyl-directed dearomatization of arenes. Our anti-1,2-dimetalation including structural and computational investigation provides a new powerful tool and unique insight in the development of organometallic chemistry and organic synthesis.