A simple, clean, and efficient approach for the one-pot synthesis of 2-oxindol-3-ylphosphonates
has been successfully developed. With 7 mol% loading of the 1,4-diazabicyclo[2.2.2]octane-based
ionic liquid catalyst, 2-oxindol-3-ylphosphonates form in good to excellent yields
within short times. This tandem reaction involves a phospha-Michael addition to the
activated alkenes, which form in situ by Knoevenagel condensation. The corresponding products are easily separated and
purified by simple crystallization. The catalyst can be recycled five times without
significant activity loss. This approach is readily amenable to large-scale synthesis.
Keywords
phosphonates - oxindoles - ionic liquid - Knoevenagel condensation - phospha-Michael
addition - tandem reaction