US EPA

1445331 

Journal Article 

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

Barakat, A; Al-Majid, AM; Mabkhot, YN; Al-Othman, ZA 

2012 

Yes 

International Journal of Molecular Sciences
ISSN: 1422-0067
EISSN: 14220067 

13 

5 

5542-5553 

22754314 

10.3390/ijms13055542 

WOS:000306186200018 

An efficient and convenient strategy for the enantioselective synthesis of enantiomerically enriched 10-ethyl-7,8-dihydro-gamma-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-gamma-ionone derivatives 6a afforded the 4-acetyl-gamma-ionone derivatives (-)-8, and the 4-hydrox-gamma-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-alpha-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 H-1, C-13 NMR, GC-MS, and IR spectrometry. These compounds represent a new class of odorants that may be of pivotal relevance in industrial perfumery. 

timberol; ionone; bio-catalysis; lipase; asymmetric catalysis