Further Developments of an Enantioselective Palladium-Catalyzed Polyene Cyclization: Surprising Solvent and Ligand Effects

Abstract

The enantioselectivity of a Pd-catalyzed domino Heck-Mizoroki cyclization is dramatically enhanced by ligand and solvent choice. Electron-deficient ligands such as (R)-DIFLUORPHOS gave 5 in %ee values ranging from 94% ee to >99% ee. EtOH was found to be superior to other solvents traditionally used in Heck-Mizoroki reactions, generally showing increases in enantioselecti­vity when compared to toluene. It is also shown that microwave heating accelerates the reaction in either solvent and allows for a longer catalyst lifetime without eroding the %ee.

palladium-catalyzed domino reaction - asymmetric catalysis - solvent effects - microwave

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