Acetals as chiral ligands for organomagnesium and organolithium compounds

Five 2-alkoxyoctahydro-7.8,8-trimethyl-4,7-methanobenzofurans were tested as additives for the enantioselective addition of butyllithium and butylmagnesium bromide to benzaldehyde. The selectivity of the reaction was determined by GC. HPLC, and by measurement of the optical rotation of the obtained 1-phenyl-1-pentanol, and the stability of the ligands under the given reaction conditions was investigated. Upon reaction with benzaldehyde, the addition of octahydro-7,8,8-trimethyl-2-(2-(phenylmethoxy)ethoxy)-4,7-methanobenzofuran to butylmagnesium bromide yielded (R)-1-phenyl-1-pentanol with 47% ee.