Stereoselective addition of allylmagnesium chloride to the CN bond of [4.3.0] boron heterobicycles

An efficient, simple protocol for the addition of allylmagnesium chloride to the CN bond of [4.3.0] boron heterobicycles afforded five new dioxaboracyclononenes 4a–e in moderate yields (51–61%). The boronates were characterized by 1H, 13C, 11B and 2D NMR experiments, and confirmed by X-ray analogues. The stereochemistry of the N–H, –CH2CHCH2 and B–Ph fusion is always cis, as established through NMR, and confirmed by X-ray structure of 4d. The structure of one of the addition products was established by X-ray analysis showing that, in the solid state, it exists as a polymeric structure formed by hydrogen bonds between the amine proton and the ester oxygen of the five-membered ring.