We report an efficient method for the direct β-acylation of 2-ylideneoxindoles with
acyl chlorides that is catalyzed by organophosphanes in the presence of base. A variety
of functionalized 2-ylideneoxindoles were prepared in moderate to good yields under
mild, metal-free conditions via a tandem phospha-Michael/O-acylation/intramolecular
cyclization/rearrangement sequence. Mechanistic investigations revealed that C–O bond
cleavage on a possible betaine intermediate is the key step for the installation of
the keto-functionality at the β-position of 2-ylideneoxindoles in a highly stereospecific
manner. The synthetic utility of this protocol could also be proven by a scale-up
reaction and synthetic transformations of the products.
Key words
β-acylation - functionalized 2-ylideneoxindoles - indolin-3-ones - phospha-Michael
addition - phosphine catalysis