Phosphotungstic Acid as an Efficient Catalyst for Allylation of Isatins and N-tert-Butyloxycarbonylamido Sulfones Under Solvent-Free Conditions

The present work demonstrates the use of phosphotungstic acid (H3PW12O40 center dot H2O) as an efficient catalyst for the allylation of isatin derivatives as well as N-tert-butyloxycarbonyl (Boc)-alpha-amido sulfones with allyltributyltin as an allylating agent under solvent-free conditions at room temperature. Excellent allylation product yields of up to 99% for the isatins substrates and good to excellent yields of up to 98% for the N-Boc a-amido sulfones were obtained. The present allylation protocol is scalable as demonstrated by allylation of N-methylisatin at 1 g scale. Based on H-1, C-13, and P-31 NMR studies a catalytic cycle was proposed for allylation of isatins as well as N-Boc amido sulfones. The allylation products N-Boc homoallyl amines were successfully epoxidized to get multifunctional compounds, which are valuable intermediates for natural products and bioactive compounds.