反应详情

The acetyl derivates of the formula XII are treated in the presence of an acid and under anhydrous conditions with ethyleneglycol and form the ketals of the formula ##STR13## wherein R2 and Y have the meanings defined above. For example, 3-acetyl-2,5-dihydro-4-hydroxy-5-methyl-1,2-thiazino[5,6-b]indole-1,1-dioxide is refluxed with ethyleneglycol in benzene as a solvent and in the presence of p-toluenesulfonic acid as a catalyst for 5 days, which yields the ethylene ketal of 2,5-dihydro-5-methyl-1,2-thiazino[5,6-b]indole-4(3H)-one-1,1-dioxide.