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Scheme 32. Organocatalytic domino 1,3-dipolar cycloaddition of butyrolactone-derived cyclic imino esters 57 and carboxylic acid-
[91]
activated chromones 64. This figure is used with permission from Georg Thieme Verlag .
Scheme 33. Evaluation of cytotoxicity toward cancer cell lines. This figure is used with permission from Georg Thieme Verlag [91] .
Scheme 34. Direct spirolactonization reaction for construction of chiral spirolactones.
Michael addition of the 3-hydroxyoxindole 69 to the (Z)-olefinic azlactone 70 and sequential ring opening
and lactonization.
