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• Barakat, A
• Al-Majid, A
• Mabkhot, Y
• Al-Othman, ZA.
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• Barakat, A
• Al-Majid, A
• Mabkhot, Y
• Al-Othman, ZA.
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• Barakat, A
• Al-Majid, A
• Mabkhot, Y
• Al-Othman, ZA.

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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

Assem Barakat* , Abdullah M. Al-Majid, Yahia Nasser Mabkhot and Zeid A. Al-Othman

Department of Chemistry, Faculty of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia

* Author to whom correspondence should be addressed.

Received: 15 March 2012; in revised form: 23 April 2012 / Accepted: 2 May 2012 / Published: 9 May 2012

Download PDF Full-Text [460 KB, uploaded 9 May 2012 12:18 CEST]

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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