anti-Diastereo- and Enantioselective Carbonyl (Hydroxymethyl)allylation from the Alcohol or Aldehyde Oxidation Level: Allyl Carbonates as Allylmetal Surrogates

Enantioselective transfer hydrogenation of carbonate la in the presence of aromatic, allylic, or aliphatic alcohols 2a-2i employing a cyclometalated iridium C,O-benzoate derived from allyl acetate, 4-cyano-3-nitrobenzoic acid and (S)-SEGPHOS delivers products of (hydroxymethyl)allylation 4a-4i in good isolated yields (60-74%), good anti-diastereoselectivities (5:1-10:1 dr) and exceptional levels of enantiocontrol (93-99% ee). Under identical reaction conditions, but in the presence of isopropanol, aldehydes 3a-3i are converted to an equivalent set of adducts 4a-4i in good isolated yields (58-74%), good anti-diastereoselectivities (4:1-14:1 dr), and exceptional levels of enantiocontrol (95-99% ee). Thus, identical sets of adducts 4a-4i are produced with equal facility from the alcohol or aldehyde oxidation level. These studies represent the first general method for enantioselective carbonyl (hydroxymethyl)allylation, a process that has no highly stereoselective counterpart in conventional allylmetal chemistry.