3-methyl-2,5-dihydrothiophene 1,1-dioxide

Conditions: temp:0.01; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: In a reaction vessel, 21.0 gms (0.1591 moles) 3-methyl sulfolene, 28.32 gms (0.1591 moles) N-bromo succinimide, 1.9 gms (0.0008 moles) benzoyl peroxide and 250 ml chlorform were combined. The resulting mixture was heated to reflux and then refluxed for 20 hours. The reaction mixture was cooled to 0° C. and then filtered to remove the succinimide. The filtrate was stripped until only a small amount of solvent remained. The remaining solids were removed by filtration, and the remainder of the solvent was stripped to give an orange oil. Ether was added to the oil. After a few minutes, the solids crystallized. Filtration and drying yielded 11.5 gms of the product. The NMR and IR spectra confirmed the structure. The resulting mixture was heated to reflux refluxed for 20 hours filtered to remove the succinimide The remaining solids were removed by filtration to give an orange oil After a few minutes the solids crystallized Filtration drying

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 5-Methyl-2H-thiopyran-1,1-dioxide is prepared in three steps from 3-methyl-3-sulfolene using the method of Gaoni, J. Org. Chem., 46 (1981) 4502. Thus, 3-methyl-3-sulfolene is first reacted with chloroform and aqueous sodium hydroxide in the presence of a quaternary ammonium salt to give the dichlorocarbene adduct. Partial dehalogenation with lithium aluminum hydride in tetrahydrofuran gives the chlorocyclopropane. Finally, base-catalyzed ring expansion with lithium diisopropylamide gives the desired thiopyran dioxide compound (see Scheme 1, above).