Size does matter. Sterically demanding metallocene-substituted 3-methylidene-oxindoles exhibit poor kinase inhibitory action

1,3-Dihydro-2H-indol-2-one (1) undergoes microwave-mediated Knoevenagel condensations with 1,2,3,4,5-pentaphenylferrocene carboxaldehyde (2b) or (eta(4)-tetraphenyl-cyclobutadiene)(eta(5)-cyclopentadienylcarboxaldehyde)cobalt (2c) to afford metallocene-substituted 3-methylidene-1,3-dihydro-2H-indol-2-one 4 or 5, respectively, in excellent yields as separable E,Z-sfereoisomeric mixtures. Both 4 and 5 exhibited poor kinase inhibition and no appreciable cytotoxicity toward a leukemia cell line, attributed to the steric bulk of the metallocene substituents.