Synthesis of Fragrance Compounds from Biorenewables: Tandem Hydroformylation-Acetalization of Bicyclic Monoterpenes

• Published in: ChemCatChem Vol. 5; no. 7; pp. 1884 - 1890
• Main Authors: de Freitas, Marina C., Vieira, Camila G., dos Santos, Eduardo N., Gusevskaya, Elena V.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01-07-2013; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Beta; fragrances; homogeneous catalysis; hydroformylation; rhodium; terpenes; VOCs; Volatile organic compounds
• ISSN: 1867-3880; 1867-3899
• DOI: 10.1002/cctc.201200948

The Rhodium‐catalyzed tandem hydroformylation–acetalization of the terpenes 3‐carene, 2‐carene, α‐pinene, and β‐pinene was studied in ethanol solutions in the presence of PPh3 or tris(O‐tert‐butylphenyl)phosphate, P(O‐o‐tBuPh)3, ligands. All these terpenes are constituents of turpentine oils obtained commercially from coniferous trees. β‐Pinene gave the corresponding aldehyde and acetal in excellent combined yields in both systems. 3‐Carene, 2‐carene, and α‐pinene, which contain sterically encumbered endocyclic double bonds, showed an extremely low reactivity with PPh3. The use of P(O‐o‐tBuPh)3 not only accelerated the hydroformylation of all four substrates remarkably but also increased the acetalization activity of the catalyst. In the Rh/P(O‐o‐tBuPh)3 system, various fragrance acetals and aldehydes were obtained from these renewable substrates in nearly quantitative combined yields. The process was performed under mild conditions, in environmentally friendly ethanol as a solvent, and in the absence of acid cocatalysts.
The sweet smell of success: Bicyclic monoterpenes, cheap biomass‐based substrates available from coniferous trees, can be transformed into valuable fragrance compounds through an efficient tandem catalytic process by using a Rh catalyst and environmentally friendly ethanol as a solvent.