A. cis- and trans-5-Methyl-2-[1-methyl-1-(phenylmethylthio)ethyl]cyclohexanone (7-benzylthiomenthone). A 1-L, three-necked, round-bottomed flask equipped with a magnetic stirring bar and a Friedrich condenser connected by its upper joint to a mineral oil bubbler through which passes nitrogen gas is charged with 500 mL of tetrahydrofuran (Note 1), 202.0 g (1.33 mol) of (+)-pulegone (Note 2), and 181.0 g (1.46 mol) of benzyl mercaptan (Note 3). The flask is flushed with nitrogen, 10 mL of aqueous 10% sodium hydroxide is added, the flask is stoppered, and the mixture is heated to reflux under a static pressure of nitrogen. After 2 hr at reflux the pale-yellow solution is allowed to cool, transferred to a 2-L separatory funnel, and washed with two 500-mL portions of saturated aqueous sodium chloride. The combined sodium chloride layers, in turn, are extracted with three 250-mL portions of ether, and the combined organic layers are dried over magnesium sulfate for 2 hr, filtered and concentrated by rotary evaporation at aspirator vacuum. The residual liquid is distilled in a good vacuum to give a fraction of bp 167–174°C (0.4 mm) weighing 325–330 g (89–90%). The product is a mixture of cis and trans isomers otherwise highly pure as evidenced by spectral analysis (Note 4).

B. 2-(1-Mercapto-1-methylethyl)-5-methylcyclohexanol (7-thiomenthol). A 5-L, three-necked, round-bottomed flask is equipped with a variable speed Hershberg stirrer and a 500-mL Dewar condenser filled with dry ice–acetone and connected by its upper joint to a mineral oil bubbler through which passes dry nitrogen gas. The flask is immersed in a dry ice–acetone bath, flushed well with nitrogen and 3000 mL of ammonia is condensed into the flask via a glass tube passed through a rubber septum in the remaining neck of the flask (Note 5). Clean sodium, 125 g (5.43 g-atom), is added slowly to the ammonia with slow stirring (Note 6). Then 250.3 g (0.906 mol) of 5-methyl-2-[1-methyl-1-(phenylmethylthio)ethyl]cyclohexanone and 72.5 mL (1.8 mol) of methanol in 625 mL of anhydrous ether (Note 7) are added dropwise via a pressure-equalized addition funnel over 5 hr to the vigorously stirred (ca. 500 rpm) solution (Note 8). Stirring is continued an additional 30 min following which 150 mL of methanol is added over 2.5 hr dropwise (to avoid a violent eruption). The solution is allowed to warm slowly (Note 9) and the addition funnel and the condenser are removed to allow the ammonia to evaporate overnight. The reaction flask is immersed in an ice bath and 700 mL of water is added cautiously over an hour to the yellow solid left by evaporation of the ammonia (Note 10). The solution is transferred to a 2-L separatory funnel and extracted with two 200-mL portions of ether, which are discarded. The aqueous layer is poured into a mixture of 500 mL of concentrated hydrochloric acid and 1000 g of ice, transferred to a 4-L separatory funnel, and extracted with four 200-mL portions of ether. The combined ether extracts are washed with 200 mL of water and 200 mL of saturated aqueous sodium chloride, dried over magnesium sulfate, and concentrated by rotary evaporation at aspirator vacuum. The residual liquid is placed under reduced pressure (0.2 mm) for 1 hr to remove the remaining solvent to give 137–140 g (80–82%) of an orange oil that is a diastereomeric mixture of which the major component constitutes 80%, as indicated by ¹³C NMR (Note 11).

C. Hexahydro-4,4,7-trimethyl-4H-1,3-benzoxathiin. To a 1-L, one-necked, round-bottomed flask equipped with a magnetic stirrer and charged with 325 mL of benzene (Note 12) is added 140.0 g (0.753 mol) of 5-methyl-2-(1-methyl-1-thioethyl)cyclohexanol, 26.0 g (0.87 mol) of paraformaldehyde (Note 13) and 1 g of p-toluenesulfonic acid monohydrate (Note 14). The flask is fitted with a Dean–Stark trap and a Friedrich condenser and the contents are refluxed for 4 hr, by which time the benzene distillate is clear. After the solution is cooled, 5 g of anhydrous potassium carbonate is added and the solution is stirred overnight, filtered, and concentrated by rotary evaporation and the residual liquid is distilled in a good vacuum to give a fraction of bp 69–94°C (0.1 mm), which weighs 130–134 g (86–89%) (Note 15). This fraction is dissolved in 250 mL of pentane, cooled to −25°C, and seeded with a crystal of the product (Note 16). Crystallization is allowed to proceed in a freezer, and collection and concentration of the mother liquor to half the original volume are carried out every other day to yield, after four crops of crystals are collected, 55–60 g (37–40%) of the spectrally pure product (Note 17).