Triphenylphosphine-Catalyzed Simple Synthesis of Vinyl-Substituted Saccharins

Saccharin (1,1-dioxo-1,2-dihydro-1 u 6 -benzo[ d ]-isothiazol-3-one) undergoes a smooth reaction with dialkyl acetylenedicarboxylates in the presence of triphenylphosphine to produce highly-functionalized salt-free sulfur-containing ylides in nearly quantitative yields. These stabilized phosphorus ylides exist as a mixture of two geometrical isomers as a result of restricted rotation around the carbon-carbon partial double bond resulting from conjugation of the ylide moiety with the adjacent carbonyl group. These ylides are converted to dialkyl 2-(1,1-dioxo-1 H -1 u 6 -benzo[ d ]-isothiazol-3-yl)-but-2-enedioates in boiling toluene.