AbstractThe 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.