Int. J. Mol. Sci. 2012, 13(5), 5542-5553; doi:10.3390/ijms13055542
Article

A Practical Chemo-enzymatic Approach to Highly Enantio-Enriched 10-Ethyl-7,8-dihydro-γ-ionone Isomers: A Method for the Synthesis of 4,5-Didehydro-α-Ionone

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Received: 15 March 2012; in revised form: 23 April 2012 / Accepted: 2 May 2012 / Published: 9 May 2012
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract: An efficient and convenient strategy for the enantioselective synthesis of enantiomerically enriched 10-ethyl-7,8-dihydro-γ-ionone isomers (R)-(+)-7, and (S)-(−)-7 are described utilizing a lipase mediated resolution protocol, and reductive elimination of the secondary allylic alcohol as the key step. The enantioselective and diastereoselective lipase kinetic acetylation of 4-hydroxy-γ-ionone derivatives 6a afforded the 4-acetyl-γ-ionone derivatives (−)-8, and the 4-hydrox-γ-ionone derivatives (+)-6a, which are suitable precursors of the desired products. Stereospecific palladium-mediated elimination of allylic acetate provides the target compounds with an excellent enantiomeric excess and yield. Additionally, the novel 4,5-didehydro-α-ionone 13 is obtained from readily prepared (2,6,6-trimethylcyclohexa-2,4-dien-1-yl) methanol 9. The structures of all newly synthesized compounds have been elucidated by 1H, 13C NMR, GC-MS, and IR spectrometry. These compounds represent a new class of odorants that may be of pivotal relevance in industrial perfumery.
Keywords: timberol; ionone; bio-catalysis; lipase; asymmetric catalysis
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MDPI and ACS Style

Barakat, A.; Al-Majid, A.M.; Mabkhot, Y.N.; Al-Othman, Z.A. A Practical Chemo-enzymatic Approach to Highly Enantio-Enriched 10-Ethyl-7,8-dihydro-γ-ionone Isomers: A Method for the Synthesis of 4,5-Didehydro-α-Ionone. Int. J. Mol. Sci. 2012, 13, 5542-5553.

AMA Style

Barakat A, Al-Majid AM, Mabkhot YN, Al-Othman ZA. A Practical Chemo-enzymatic Approach to Highly Enantio-Enriched 10-Ethyl-7,8-dihydro-γ-ionone Isomers: A Method for the Synthesis of 4,5-Didehydro-α-Ionone. International Journal of Molecular Sciences. 2012; 13(5):5542-5553.

Chicago/Turabian Style

Barakat, Assem; Al-Majid, Abdullah M.; Mabkhot, Yahia Nasser; Al-Othman, Zeid A. 2012. "A Practical Chemo-enzymatic Approach to Highly Enantio-Enriched 10-Ethyl-7,8-dihydro-γ-ionone Isomers: A Method for the Synthesis of 4,5-Didehydro-α-Ionone." Int. J. Mol. Sci. 13, no. 5: 5542-5553.

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