Iridium-Catalyzed anti-Diastereo- and Enantioselective Carbonyl (Trimethylsilyl)allylation from the Alcohol or Aldehyde Oxidation Level

摘要

Using the ortho-cyclometalated π-allyl iridium precatalyst (R)-I derived from [Ir(cod)Cl]₂, 4-cyano-3-nitrobenzoic acid, (R)-SEGPHOS, and allyl acetate, enantioselective transfer hydrogenation of α-(trimethylsilyl)allyl acetate in the presence of aldehydes 2a−i mediated by 2-propanol delivers products of (trimethylsilyl)allylation 4a−i in good isolated yields and with exceptional levels of anti-diastereoselectivity and enantioselectivity (90−99% ee). In the absence of 2-propanol, but under otherwise identical reaction conditions, carbonyl (trimethylsilyl)allylation is achieved directly from the alcohol oxidation level to furnish an equivalent set of adducts 4a−i with roughly equivalent isolated yields and stereoselectivities. To evaluate the synthetic utility of the reaction products 4a−i, adduct 4g was converted to the 1,4-ene-diol 5g via dioxirane-mediated oxidative desilylation with allylic transposition, the allylic alcohol 6g via protodesilylation with allylic transposition, and the γ-lactam 7g via chlorosulfonyl isocyanate-mediated cycloaddition.