Microwave-Induced Stereoselective Conversion of Dialkyl 2-(1,1,3-Trioxo-1,3-dihydro-2 H -1,2-Benzisothiazol-2-yl)-3-(triphenylphosphoranylidene)succinates to Dialkyl 2-(1,1,3-Trioxo-1,3-dihydro-2 H -1,2-benzisothiazol-2-yl)-2-butendioates in the Presence of Silica-Gel Powder in Solvent-Free Conditions

Protonation of the highly reactive 1:1 intermediates produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates by saccharin leads to vinyltriphenylphosphonium salts, which undergo an addition reaction with a counter anion in CH 2 Cl 2 at r.t. to produce the corresponding stabilized phosphorus ylides. Silica-gel powder was found to catalyze the stereoselective conversion of the stabilized phosphorus ylides to the corresponding electron-poor N-vinylated isothiazoles in solvent-free conditions under thermal and microwave irradiation in fairly good yields.