Green synthesis of novel isatin thioketal derivatives under solvent-free conditions

A new series of spiro[[1,3]dithiolane-2,3'-indolines]-2'-one derivatives was synthesized using Michael addition reaction of spiro[[1,3]dithiolane-2,3'-indolin]-2'-one to various alpha,beta-unsaturated esters as well as direct alkylation of this compound with alkyl dihalides. Michael reaction of spiro [[1,3]dithiolane-2,3'-indolin]-2'-one and alpha,beta-unsaturated esters produced related Michael adduct in the presence of tetrabutylammonium bromide and base 1,4-diazabicyclo[2.2.2]octane in good to excellent yields at 80 degrees C under solvent-free conditions. Also, direct alkylation of spiro[[1,3]dithiolane-2,3'-indolin]-2'-one by dihaloalkanes in the presence of base K2CO3 afforded the corresponding products in good yields under the same conditions.