Stereoselective Boron-Masking of polyBorylated-Alkenes: An Access to Stereodefined polyMetalloid Alkenes

Polyborylated-alkenes are valuable reagents in modern organic synthesis, providing access to a wide array of transformations, including the construction of multiple C–C and C–heteroatom bonds. However, because they contain similar boryl groups, many times their transformation faces the main challenge in controlling the chemo-, regio- and stereoselectivity. One way to overcome these limitations is by installing different boron groups that can provide an opportunity to tune their reactivity toward better chemo-, regio- and stereoselectivity. However, the preparation of polyborylated-alkenes containing different boryl groups has been rare. Herein we report concise, highly site-selective, and stereoselective boron-masking strategies of polyborylated alkenes. This was achieved by designed stereoselective "trifluorination" and “MIDA-ation” reactions of readily available starting polyborylated alkenes. Additionally, the trifluoroborylated-alkenes underwent a stereospecific interconversion to Bdan-alkenes. These transition-metal free reactions provide a general and efficient method for the conversion of polyborylated alkenes to access 1,1-di-, 1,2-di-, 1,1,2-tris-(borylated) alkenes containing BF3Cs, Bdan, and BMIDA, a family of compounds that currently lack efficient synthetic access. Moreover, tetraborylethene underwent the metal-free “MIDA-ation” reaction to provide the mono BMIDA tetraboryl alkene selectively. Given its simplicity and versatility, these novel stereoselective boron-masking approaches hold great promise for organoboron synthesis and will result in more novel transformations.