Synthesis of cis-Hedione® and Methyl Jasmonate via Cascade Baylis–Hillman Reaction and Claisen Ortho Ester Rearrangement
✍ Scribed by Christian Chapuis; George H. Büchi; Hans Wüest
- Publisher
- John Wiley and Sons
- Year
- 2005
- Tongue
- German
- Weight
- 220 KB
- Volume
- 88
- Category
- Article
- ISSN
- 0018-019X
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✦ Synopsis
Abstract
The exocyclically unsaturated conjugated keto esters 10, obtained via a Claisen ortho ester rearrangement of the allylic hydroxy ketones 9, were either directly hydrogenated or partially isomerized into the endocyclically unsaturated tetrasubstituted didehydrojasmonoid intermediates 14, prior to a more selective hydrogenation with Pd/C in cyclohexane to the disubstituted oxocyclopentaneacetates 15 (Scheme 2). The key intermediates 9 were obtained either by a four‐step sequence, including acetal protection/deprotection from enone 1, in the specific case of hydroxy ketone 9a (Scheme 1), or more directly and generally by a Baylis–Hillman reaction from cyclopent‐2‐en‐1‐one (16) and the appropriate aldehydes 17 (Scheme 2). The judicious choice of these aldehydes opens versatile modifications for the stereoselective introduction of the partially cis‐ or epimerized trans‐C(2) jasmonoid side chain, while the Baylis–Hillman reaction, catalyzed by chiral [1,1′‐binaphthalene]‐2,2′‐diols (BINOLs) 19 (Scheme 3), may be efficiently conducted in a one‐pot cascade fashion including the ortho ester Claisen rearrangement.