Straightforward Access to Terpene-Based 1,2-Diols and Their Acetals as Fragrance Ingredients

Numerous terpenes and their derivatives are potent fragrances e.g., cis-cedrane-8,9-diol is the key intermediate for the synthesis of the corresponding acetonide, which is an extremely powerful semisynthetic aroma molecule. The current production process starting from naturally occurring sesquiterpene (-)-α-cedrene yields the acetonide in an overall yield <20%. Several cis-dihydroxylation methods were tested for the direct conversion of cedrene to the corresponding diol. Simple potassium permanganate proved to be the most efficient, leading to cis-cedrane-8,9-diol in up to 76% yield under alkaline conditions. This methodology was applicable to other terpene based substrates yielding the corresponding 1,2-diols in up to 83%. The resulting terpene 1,2-diols were successfully converted into the corresponding acetonides in up to 92% yield and their olfactive properties were evaluated.