1 Supporting Information Chloromethanesulfonylethene and Dichloromethanesulfonylethene: New Reagents for Tandem Diels-Alder-Ramberg-Bäcklund Reactions Eric Block*, Hak Rim Jeon, Shao-Zhong Zhang, and Evgeny Dikarev β-Chlorosulfides may be toxic on inhalation, ingestion or skin contact. These compounds should only be handled in a well-ventilated hood using rubber gloves. All glassware used should be rinsed with bleach (“Clorox”) immediately after use. ClCH 2 SCl Chloromethanesulfenyl Chloride (5) 4 . A magnetic stirrer-equipped flask was charged with CH 2 Cl 2 (60 mL) and Me 2 S 2 (9.16 g, 97 mmole), the mixture was cooled to –78 o C and Cl 2 gas was bubbled through slowly using a 9 mm glass tube (a solid was formed plugging smaller bore tubes). The mixture turned red-orange and a colorless solid (CH 3 SCl 3 ) appeared. The mixture turned into a milky, yellow-white slurry, which continued to thicken and lighten until the solution became saturated with chlorine, at which time the mixture took on a yellow-green color. Addition of Cl 2 was stopped and a reflux condenser with drying tube was fitted to the flask. Decomposition of CH 3 SCl 3 was promoted by warming the flask to room temperature. An orange liquid formed as HCl was evolved. Concentration in vacuo yielded the title compound as a malodorous, lachrymatory oil (20 g, 88%) which was used without further purification; 1 H NMR (300 MHz, CDCl 3 ) δ 5.12 (s); 13 C NMR (75 MHz, CDCl 3 ) δ 54.8.