New, Improved Procedure for the Synthesis of Structurally Diverse N-Spiro C2-Symmetric Chiral Quaternary Ammonium Bromides

Selective, direct ortho magnesiation of (S)-2,2'-bis(isopropoxycarbonyl)-1,1'-binaphthyl (6) has been achieved under mild conditions, using magnesium bis(2,2,6,6-tetramethylpiperamide) [Mg(TMP)(2)]. In combination with the subsequent reaction with the appropriate electrophiles, bromine and iodine, this method constitutes a key step in establishing a new and concise synthetic route to a wide variety of N-spiro C(2)-symmetric chiral quaternary ammonium bromides of type 1.