CuBr₂-Catalyzed adamantanone-2 ketalization in the synthesis of practically important cyclic ketals.

Cyclic adamantanone ketals have pleasant odors and are of interest in the cosmetic field as fragrances. They are usually prepared by condensation of adamantanone-2 with 1,2-ethanediol and 1,2-propanediol in the presence of catalytic amounts of strong Bronsted or Lewis acids. These reactions are often carried out using Dean-Stark trap and azeotropic removal of water to prevent hydrolysis of the product. Sometimes the reactions require high temperatures, long reaction times, or are difficult to perform. We first developed a CuBr2-catalyzed method for ketalization of adamantanone-2 with 1,2-ethanediol and 1,2-propanediol. The reaction takes place in 1-2 hours at a temperature of 40-100 ^oC, giving the corresponding cyclic ketals in high yields. 4-Мethylspiro[1,3-dioxolane-2,2'-tricyclo[3.3.1.13,7]decane] has a persistent fruit-apple/honey smell and can be used to flavor shampoos, gels, soaps. Spiro[1,3-dioxolane-2,2'-tricyclo[3.3.1.13,7]decane] has a faint note of sage and thyme, as well as a persistent note of freshness, and can be used to flavor toothpaste and mouthwash.