- 172. β-Cleavage of Bis(homoallylic) Potassium Alkoxides. Two-Step Preparation of Propenyl Ketones from Carboxylic Esters. Synthesis of ar-Turmerone, α-Damascone, β-Damascone, and β-Damascenone
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The transformation of 36 bis(homoallylic) alcohols VII to alkenones IX and X via β-cleavage of their potassium alkoxides VIIa in HMPA has been investigated (cf.Scheme 2).These studies have established an order of β-cleavage for 2-propenyl, 1-methyl-2-propenyl, 2-methyl-2-propenyl, 1,1-dimethyl-2-propenyl, and benzyl groups in alkoxides 49a-56a and have allowed a comparison between the β-cleavage reaction and the oxy-Cope rearrangement in alkoxides 74a-83a.As illustrative synthetic applications, a two-step preparation of propenyl ketones 15-42 from carboxylic esters is described, together with syntheses of ar-turmerone (48), α-damascone ((E)-71), β-damascone ((E)-109), and β-damascenone ((E)-111).
- Snowden, Roger L.,Linder, Simon M.,Muller, Bernard L.,Schulte, Karl H.
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p. 1858 - 1878
(2007/10/02)
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- Synthesis of (E)-1-Propenyl Ketones from Carboxylic Esters and Carboxamides by Use of Mixed Organolithium-Magnesium Reagents
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The novel reagents formed by combination of allylmagnesium chloride and a strong non-nucleophilic lithium base (LiNR2) convert non- or slowly enolizable carboxylic esters or carboxamides into 2-propenyl ketones which are protected from further reaction by their in situ conversion into enolates.This modified Grignard reaction is applied to efficient syntheses of α-damascone, β-damascone, β-damascenone, and various other (E)-1-propenyl ketones.
- Fehr, Charles,Galindo, Jose
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p. 228 - 235
(2007/10/02)
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- Photochemistry of dienones. Part 12. Photochemistry of (E)-α- and (E)-β-damascone
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The photochemistry of (E)-α- and (E)-β-damascone has been studied.Upon triplet-sensitized irradiation, both compounds exclusively undergo (E)-(Z) isomerization. (E)-β-damascone, upon direct irradiation with λ 254, 300 or 350 nm in non-alcoholic solvents, exhibits only (E)-(Z) isomerization.However, in an alcoholic solvent, direct irradiation induces cyclization and subsequent solvent incorporation, with formation of exo-8-alkoxy-1,5,5-endo-9-tetramethyl-cis-bicyclononan-7-one (12). (E)-α-damascone, upon direct irradiation, exhibits α-cleavage with subsequent formation of the 1,3-acyl shift product, and equal amounts of the dimerization products of the allylic radical, viz. 9 and 10.The 1,3-acyl shift product again undergoes photo-α-cleavage and the only products, upon prolonged irradiation, are the bicyclohexenyls 9 and 10.
- Visser, Cornelis P.,Cerfontain, Hans
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p. 307 - 311
(2007/10/02)
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