Preparation of Primary and Secondary Dialkylmagnesiums by a Radical I/Mg‐Exchange Reaction Using sBu2Mg in Toluene

The treatment of primary or secondary alkyl iodides with sBu2Mg in toluene (25–40 °C, 2–4 h) provided dialkylmagnesiums that underwent various reactions with aldehydes, ketones, acid chlorides or allylic bromides. 3‐Substituted secondary cyclohexyl iodides led to all‐cis‐3‐cyclohexylmagnesium reagents under these exchange conditions in a highly stereoconvergent manner. Enantiomerically enriched 3‐silyloxy‐substituted secondary alkyl iodides gave after an exchange reaction with sBu2Mg stereodefined dialkylmagnesiums that after quenching with various electrophiles furnished various 1,3‐stereodefined products including homo‐aldol products (99 % dr and 98 % ee). Mechanistic studies confirmed a radical pathway for these new iodine/magnesium‐exchange reactions. Primary and secondary dialkylmagnesium reagents were prepared in toluene by the reaction of sBu2Mg with alkyl iodides (25–40 °C, 1–4 h). Stereoconvergent I/Mg‐exchanges were observed for secondary cyclohexyl iodides leading after quenching reactions to products with high enantio‐ and diastereoselectivity, including homo‐aldol products. Mechanistic studies confirmed radical pathways for these exchanges.