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Saccharin derivative synthesis via [1,3] thermal sigmatropic rearrangement: a multistep organic chemistry experiment for undergraduate students
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Saccharin (1,2-benzisothiazole-3-one 1,1-dioxide) is an artificial sweetener used in the food industry. It is a cheap and easily available organic compound that may be used in organic chemistry laboratory classes for the synthesis of related heterocyclic compounds and as a derivatizing agent. In this work, saccharin is used as a starting material in a sequential synthesis designed for completion in three laboratory periods of 4 h each. This synthesis includes two nucleophilic substitutions, namely, the transformation of saccharin into saccharyl chloride and the addition of cinnamyl alcohol to saccharyl chloride (3-chloro-1,2-benzisothiazole 1,1-dioxide) to yield O-cinnamylsaccharin [(E)-3-(3-phenylprop-2-enoxy)-1,2-benzisothiazole 1,1-dioxide]. The third reaction is the isomerization of O-cinnamylsaccharin into N-cinnamylsacchain [2-(3-pheny1-2(E)-propen-1-yl)]-1,2-benzisothiazole-3(2H)-one 1,1-dioxide], a [1,3] sigmatropic rearrangement. The products are characterized using melting point, IR, and H-1 NMR spectroscopy. These experiments allow students to acquire experience in a multistep synthesis, practice the most typical laboratory scale synthesis, isolation, purification, and analytical methods, and think through and discuss the mechanisms of the intervening reactions.