The general procedure for the synthesis of 2,2-dimethyltetrahydropyran-4-one from dimethyl(vinyl)ethynylmethanol was as follows: diethyl vinyl ethynylmethanol (230 g) was slowly added to a solution containing LA g aqueous solution and SULTUNC acid (5%, 0.6 mL), the reaction was maintained under vigorous stirring for 1 h, and the temperature was slowly elevated to 85 °C. The reaction was carried out in the following manner. Sulfate (18 g) was added in batches over 4 hours at 85 °C. Upon completion of the reaction, the upper liquid layer was separated and the lower layer was neutralized with potassium carbonate and subsequently extracted twice with ether. The separated upper liquid was combined with the ether extract, washed sequentially with potassium carbonate solution and water, and dried with magnesium sulfate. After evaporation to remove the ether, the residue was subjected to vacuum distillation and the 168-175 °C fraction was collected to give the target product 2,2-dimethyltetrahydropyran-4-one (140 g, 53% yield).
Anhydrous toluene (150 mL) and sodium (11 g) were heated to reflux, stirred and cooled to room temperature. To this system was slowly added a solution (5-6 mL) of ethyl chloroacetate (63 g, 0.5 mol) and 2,2-dimethyltetrahydropyran-4-one (64 g, 0.5 mol) prepared above. The remaining solution was added dropwise at 23°C over 3-4 hours. When the sodium was completely consumed, anhydrous methanol (8 mL) was added. The reaction mixture was quenched by careful pouring into ice water (100 mL), ether was added and the upper organic phase was separated. The aqueous layer was extracted with ether, all ether extracts were combined, washed with water and dried with magnesium sulfate. After evaporation of the solvent, the residue was subjected to vacuum distillation (101 °C, 2 mmHg) to give the intermediate product (74 g, 70% yield).
Ethyl 5,5-dimethyl-1,6-dioxapropane-2,5-octane-2-carbonate (214 g, 1 mol) was added to an aqueous solution (30 mL) of sodium hydroxide (40 g, 1 mol) and stirred at 30 °C for 30 min. After continued stirring for 2 hours, water (200 mL) was added to dissolve the precipitate. The resulting aqueous solution of sodium 5,5-dimethyl-1,6-dioxane-2,5-octane-2-carbonate was heated to 90 °C and 15-20% hydrochloric acid (1 mol) was added dropwise at this temperature over 4 hours. The aldehyde generated during the process was distilled, the reaction solution was saturated with NaCl and extracted with ether (3 x 200 mL). The organic extracts were combined, dried with anhydrous magnesium sulfate and concentrated under vacuum. The residue was distilled under vacuum (61 °C, 7 mmHg) to give the aldehyde intermediate (80 g, 55% yield).
To the cooled 2,2-dimethyl-4-formyltetrahydropyran (17 g, 0.5 mol) was added a solution of potassium permanganate (79 g, 0.5 mol) in water (1 L), keeping the reaction temperature at 25°C. After 6 hours of reaction, the MnO2 was removed by filtration and washed with water. The filtrates were combined and evaporated to a volume of 175 mL, acidified with HCl and extracted with ether. The organic phase was dried with anhydrous magnesium sulfate and concentrated under vacuum. The residue was distilled under vacuum (123 °C, 5 mmHg) to give the target carboxylic acid (71 g, 90% yield).
The product of Example 82 was prepared by combining tert-butyl 3-tert-butyl-1-OXA-8-azaspiro[4.5]decane-8-carboxylate with the carboxylic acid according to the method of Examples 78 and 71 in U.S. Patent 6,489,354 and the steps of Example 11. Mass spectrometry analysis showed m/e = 585 (M + 1).
