A Practical Chemo-enzymatic Approach to Highly Enantio-Enriched 10-Ethyl-78-dihydro-γ-ionone Isomers: A Method for the Synthesis of 45-Didehydro-α-Ionone

摘要

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.