1.In Situ Solid-State (13)C NMR Observation of Pore Mouth Catalysis in Etherification of β-Citronellene with Ethanol on Zeolite Beta.
Radhakrishnan S1, Goossens PJ1, Magusin PC1, Sree SP1, Detavernier C2, Breynaert E1, Martineau C3,4, Taulelle F1,3, Martens JA1. J Am Chem Soc. 2016 Mar 2;138(8):2802-8. doi: 10.1021/jacs.5b13282. Epub 2016 Feb 17.
The reaction mechanism of etherification of β-citronellene with ethanol in liquid phase over acid zeolite beta is revealed by in situ solid-state (13)C NMR spectroscopy. Comparison of (13)C Hahn-echo and (1)H-(13)C cross-polarization NMR characteristics is used to discriminate between molecules freely moving in liquid phase outside the zeolite and molecules adsorbed inside zeolite pores and in pore mouths. In the absence of ethanol, β-citronellene molecules enter zeolite pores and react to isomers. In the presence of ethanol, the concentration of β-citronellene inside zeolite pores is very low because of preferential adsorption of ethanol. The etherification reaction proceeds by adsorption of β-citronellene molecule from the external liquid phase in a pore opening where it reacts with ethanol from inside the pore. By competitive adsorption, ethanol prevents the undesired side reaction of β-citronellene isomerization inside zeolite pores.
2.Thermal isomerization of (+)-cis- and (-)-trans-pinane leading to (-)-beta-citronellene and (+)-isocitronellene.
Stolle A1, Ondruschka B, Bonrath W, Netscher T, Findeisen M, Hoffmann MM. Chemistry. 2008;14(22):6805-14. doi: 10.1002/chem.200800298.
Catalyzed and uncatalyzed rearrangement reactions of terpenoids play a major role in laboratory and industrial-scale synthesis of fine chemicals. Herein, we present our results on the thermally induced isomerization of pinane (1). Investigation of the thermal behavior of (+)-cis- (1 a) and (-)-trans-pinane (1 b) in a flow-type reactor reveals significant differences in both reactivity and selectivity concerning the formation of (-)-beta-citronellene (2) and (+)-isocitronellene (3) as main products. Possible explanations for these results are discussed on the basis of reaction mechanism and ground-state geometries for 1 a and 1 b. To identify side reactions caused from ene cyclizations of 2 and 3, additional pyrolysis experiments were conducted that enabled the identification of almost all compounds in the network of C(10)H(18)-hydrocarbon products formed from 1.
3.Regioselective biotransformation of (+)- and (-)-citronellene by the larvae of common cutworm ( Spodoptera litura ).
Miyazawa M1, Marumoto S, Masuda A, Kano H, Takechi H. J Agric Food Chem. 2009 Sep 9;57(17):7800-4. doi: 10.1021/jf9009069.
Terpenoids, which have many biological activities and have occurred widely in nature, can be artificially synthesized. However, regioselective oxidation of terpenoids is difficult by chemical methods. In this study, (+)- and (-)-citronellene were biotransformed with Spodoptera litura to define the mechanism of metabolism of citronellene and gain a new natural terpenoid. (+)-Citronellene was converted to (2S,3S)-3,7-dimethyl-6-octene-1,2-diol and (2R,3S)-3,7-dimethyl-6-octene-1,2-diol (89.7%), (3S,6S)-(-)-3,7-dimethyl-1-octene-6,7-diol (3.8%), (3S)-(6E)-(+)-3,7-dimethyl-1,6-octadien-8-ol (4.2%), and (3S)-(6E)-(+)-3,7-dimethyl-1,6-octadien-8-oic acid (2.3%). In contrast, (-)-citronellene was converted to (2R,3R)-3,7-dimethyl-6-octene-1,2-diol and (2S,3R)-3,7-dimethyl-6-octene-1,2-diol (56.3%), (+)-iridan-7,8-diol (3.5%), and (3R)-(6E)-(-)-3,7-dimethyl-1,6-octadien-8-oic acid (40.2%). The main metabolic pathway of (+)- and (-)-citronellene by larvae of S.