Stereoselective Synthesis of Trisubstituted Olefins by a Directed Allylic Substitution Strategy

New methodology for the stereoselective synthesis of trisubstituted olefins is presented. The use of ortho ‐diphenylphosphanyl benzoate ( o ‐DPPB) as a directing leaving group for copper‐mediated allylic substitution with Grignard reagents allowed for the stereoselective construction of a wide range of E olefins, without the need for an adjacent electron‐withdrawing group. Our modular three‐step approach toward trisubstituted alkenes commenced with geminal α‐methylene aldehydes. Addition of an organometallic reagent and introduction of the o ‐DPPB group by esterification was followed by the o ‐DPPB‐directed copper‐mediated allylic substitution with a Grignard reagent to furnish stereodefined trisubstituted olefins. Additionally, incorporation of a stereocenter from the chiral pool allowed the preparation of an enantiomerically pure olefin that bore three alkyl substituents in high E / Z selectivity.