Synthesis of Sulfur Heterocycles by Thio-Claisen Rearrangement

7-Chloro-4-hydroxydithiocoumarin was alkylated with allylic halides under phase transfer catalysis condition in the presence of TBAB or BTEAC in chloroform-aqueous NaOH (1%) at room temperature. 2,3-Dichloroprop-2-ene on similar treatment with 7-chloro-4-hydroxydithiocoumarin afforded 2-methylthieno[2,3-b]thiochromen-4-one in 65% yield. The S-alkylated thiochromen-4-ones were then refluxed in quinoline to give 7-chloro-2,3-dihydrothieno[2,3-b]thiochromen-4-ones or 7-chloro-2,3,4-trihydrothiopyrano[2,3-b]thiochromen-5-ones or 7-chloro-2,3-dihydro-3-vinylthieno[2,3-b]thiochromen-4-one.