Synthesis of trans-1,2-dimetalloalkenes through reductive anti-dimagnesiation and dialumination of alkynes

Abstract

Polar reactive organometallic species have been key reagents in synthesis for more than a century. Stereodefined 1, 2-dimetallated alkenes offer promising synthetic utility; however, few methods are available for their preparation due to their relatively low stability. Here we report the reductive anti-1, 2-dimetallation of alkynes to stereoselectively generate trans-1, 2-dimagnesio- and 1, 2-dialuminoalkenes, which are stable and have been demonstrated in organic synthesis. These stereodefined 1, 2-dimetallated alkenes are prepared through the use of a sodium dispersion as a reducing agent, and organomagnesium and organoaluminium halides as reduction-resistant electrophiles. Highly nucleophilic 1, 2-dimagnesioalkenes serve as dual Grignard reagents and have been demonstrated to react with various electrophiles to afford anti-difunctionalized alkenes. The 1, 2-dialuminoalkenes react with paraformaldehyde with dearomatization of the aryl moieties to form the corresponding dearomatized 1, 4-diols, with the overall reaction being regarded as alkynyl-directed dearomatization of arenes. X-ray crystallographic analysis further supports the formation of trans-1, 2-dimagnesio- and 1, 2-dialuminoalkenes, with computational studies providing insight into the mechanism of dearomative difunctionalization.