Synthesis of fragrance compounds from acyclic monoterpenes : rhodium catalyzed hydroformylation and tandem hydroformylation/acetalization of linalool and B-citronellene.

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2013
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Rhodium-catalyzed hydroformylation of acyclic monoterpenic compounds, i.e., linalool and _- citronellene, was studied in toluene and ethanol solutions in the presence of PPh3 or P(O-o-tBuPh)3 ligands. Although both substrates have a monosubstituted terminal double bond, they show different behavior under the hydroformylation conditions. In toluene, linalool gave almost quantitatively a cyclic hemiacetal; whereas the hydroformylation of _-citronellene resulted in two isomeric aldehydes also in a nearly quantitative combined yield. The reactions occurred approximately two times faster in ethanol than in toluene giving the corresponding acetals even in the absence of additional acid co-catalysts. In the absence of phosphorous ligands, linalool (differently from _-citronellene) was very resistant to hydroformylation probably due to the binding with rhodium through both the double bond and the hydroxyl group to form stable chelates. The P(O-o-tBuPh)3 ligand exerted a remarkable effect on the reactivity of both substrates accelerating the reactions by 5–20 times as compared to the system with PPh3. Several fragrance compounds were obtained in high yields through a simple one-pot procedure starting from the substrates easily available from natural bio-renewable resources.
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Acetalization, Citronellene, Hydroformylation, Linalool, Monoterpenes
Citação
VIEIRA, C. G.; SANTOS, E. N. dos; GOUSSEVSKAIA, E. V. Synthesis of fragrance compounds from acyclic monoterpenes: rhodium catalyzed hydroformylation and tandem hydroformylation/acetalization of linalool and B-citronellene. Applied Catalysis. A, General, v. 466, p. 208-215, 2013. Disponível em: <http://www.sciencedirect.com/science/article/pii/S0926860X13003785>. Acesso em: 22 mai. 2015.