Substrate‐Directed Diastereoselective Hydroformylations, 1. Substrate‐Directed Diastereoselective Hydroformylation of Methallylic Alcohols – Development of an Efficient Catalyst‐Directing Group for Rhodium‐Catalyzed Hydroformylation

The development of an efficient catalyst‐directing group based on ortho ‐diphenylphosphanyl benzoate ( o ‐DPPB) for the substrate‐directed, diastereoselective hydroformylation of methallylic alcohols 5 is described. The hydroformylation of methallylic o ‐DPPB esters 9 provides the corresponding syn ‐aldehydes 10 with diastereoselectivities of up to 96:4. A specific steric demand of the substituent at the stereogenic center of the methallylic derivatives 9 was found to be necessary to achieve a high degree of stereoselectivity. Experiments have been performed that prove that the o ‐DPPB group acts as a catalyst‐directing group by reversibly coordinating to the catalyst. The removal of the o ‐DPPB group was accomplished by means of alkaline hydrolysis, thereby furnishing the lactols 6 . Oxidation of 6 provides the corresponding γ‐lactones 7 .