Organocatalytic Asymmetric Michael Addition of Oxazolones to Arylsulfonyl Indoles: Facile Access to<i>syn</i>-Configured α,β-Disubstituted Tryptophan Derivatives
Enantioselective Michaeladdition of oxazolones to in situ generated vinylogous imine intermediates is reported. A series of optically active 3-alkylindole derivatives with adjacent quaternary and tertiary stereocenters was obtained. The resulting adducts can readily be converted into syn-configured α,β-disubstitutedtryptophanderivatives without compromising the stereoselectivities.
An efficient organocatalyzed enantioselective hydrophosphinylation of indole-derived vinylogous imines generated in situ from sulfonyl indoles has been developed. Using quinine-derived bifunctional thiourea as the catalyst, a wide range of structurally diverse chiral 3-(1-diphenylphosphoryl-arylmethyl)indoles were obtained with good to excellent results (up to 99% yield and 99% ee). This method represents