Controlled Generation of Three Contiguous Stereocentres in the Michael Addition of 1-Pyrrolidinocyclohexene to (E)-(1-Methyl-2-oxoindolin-3-ylidene)acetophenone

Addition of 1-pyrrolidinocyclohexene to (E)-(1-methyl-2-oxoindolin-3-ylidene)acetophenone followed by acid hydrolysis was diastereoselectively controlled to give (±)-7a (3R*,1′S*,2′S*) or (±)-7b (3S*,1′R*,2′S*), the structures of which were supported by 1H NMR spectroscopic data and corroborated by X-ray diffraction analysis. The change in configuration at the C-2′ centre greatly affected the geometries of the two diastereomers, both in solid and in solution. An explanation of the observed diastereoselectivity is provided. An approach to the N-methylwelwitindolinone C skeleton from 7b as a starting material, by insertion of a rhodium carbenoid into the C(4)−H indole position, was abandoned because of the initial experimental results, which are also described. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)