Dimethyl Sulfide → 6,6-Dimethylbicyclo[3.1.1]heptane-2,4-dione

A solution of 6,6-dimethyl-4-methylene-bicyclo[3.1.1]heptan-2-one (2(10)pinen-4-one, 6.8 g, 45.3 mmol) in dry methanol (300 mL) under a nitrogen atmosphere was cooled to −78° C. in a dry ice/acetone bath. The stirred reaction was treated with ozone for 20 minutes, during which time the solution turned a light blue color, indicating accumulation of ozone and completion of the reaction. The reaction was purged with oxygen (5 minutes), followed by nitrogen (10 minutes) at −78° C., and then dimethyl sulfide (5.0 ml, 68.2 mmole) was added dropwise via a syringe. The resulting reaction mixture was stirred overnight, during which time it came up to room temperature. Methanol was removed on a rotary evaporator, and the residue was partitioned between ethyl acetate (300 mL) and water (300 mL). The aqueous layer was extracted with two additional portions of ethyl acetate (300 mL), and the combined organic layers were dried over anhydrous sodium sulfate and concentrated on a rotary evaporator. The desired product was isolated by column chromatography on silica gel (20% ethyl acetate/hexane) to gave the desired product as a white solid (5.7 g; 83% yield), mp=80–81° C.; MS (−) ESI m/z=151 (M−H)−.