A. Tortajada

Flavones, sesquiterpene lactones and glycosides isolated from Centaurea aspera var. Stenophylla

Abstract From the alcoholic extract of Centaurea aspera var. stenophylla benzoic acid, p-hydroxybenzoic acid, apigenin, 6-methoxyluteolin, 11,13-dehydromelitensin, melitensin, stenophyliolide, ethyl-7-O-apigenin-glucuronate and the glucosides of sitosterol and stigmasterol were isolated and characterized. Stenophyllolide was shown to be 9,15-dihydroxygermacra-1(10),4,11-trien-12,6-olide.

Dienediolates of unsaturated carboxylic acids in synthesis. Aldehydes and ketones from alkyl halides, by ozonolysis of β,γ-unsaturated α-alkyl carboxylic acids. The role of a tertiary amine in the cleavage of ozonides

Abstract A convenient two-step procedure for a two carbon homologative conversion of alkyl halides into aldehydes and methyl ketones by α-alkylation of unsaturated carboxylic acids, followed by ozonolysis is developed and applied to the synthesis of ω-chloro aldehydes. Triethylamine is superior to dimethyl sulfide or triphenylphosphine for cleavage of the ozonides, except when aldol condensation side reactions require use of protic solvents and iodide salts. Cleavage of the ozonides by triethylamine is shown to occur mainly through a reductive process.

13C NMR studies of dianions of unsaturated carboxylic acids

Abstract 13C NMR Spectra of the dianions Li2-n resulting from double deprotonation of unsaturated carboxylic acids 1 to 6 by lithium dialkylamides, are examined. Higher field resonance for C2 than for C4 atoms are observed, which reveal higher elctron density at C2 than at C4, in agreement with the kinetic α-regioselectivity exhibited by these dianions on reaction with electrophiles.

Trienediolates of hexadienoic acids in synthesis. synthesis of retinoic and nor-retinoic acids.

Abstract Double deprotonation of either (E,E)-3-methyl-2,4-hexadienoic acid 2, or 4,6-dimethyldihydro-2-pyrone 3 generates apparently the same lithium trienediolate, which affords ω-hydroxy acids 9 on reaction with ketones 7. Hydroxy acids 9 are easily dehydrated to octatrienoic acids 5, which are structurally related to retinoic acid. Similarly, sorbic acid 1 leads to nor-retinoic acid analogs 6.

Silver ion oxidative coupling of diene and triene-diolates of unsaturated carboxylic acids: a facile synthesis of octa- and dodeca-dienedioic acids

Abstract Polyunsaterated dicarboxylic acids 3 and 5 are very easily prepared by oxidative coupling of lithium diene- and triene-diolates 1 and 2 with silver nitrate.

Trienediolates of hexadienoic acids in synthesis. Addition to unsaturated ketones. A convergent approach to the synthesis of retinoic acids

Abstract The regioselectivity of the addition of the lithium trienediolates generated from hexa-2,4dienoic acids 1 and 2 or the dihydropyran-2ones 4 and 5 to unsaturated ketones 6 is studied. Equilibration conditions favour reaction of the trienediolates through their ω carbon, and the ketones according to 1,2- and 1,4-additions. β-Ionone 6a and the aryl-butenone 6b lead to the 1,2-ω-adducts 8 , which undergo a facile acid catalyzed dehydration to retmoic acids 11 . On reaction with the unsaturated ketone 6b or with the aryl ketones 21 , the trimethyldihydropyran-2one S leads to γ-adducts derived from deprotonation of the chain methyl mbstituent along with the 1,4-ω-adducts.

Dienediolates of Unsaturated Carboxylic Acids in Synthesis. Tandem Michael Diechmann Synthesis of Substituted 2-Cyclohexenones

Abstract 3,5-Disubstituted 2-Cyclohexenones are prepared by tandem Michael-Dieckmann addition of lithium dienediolates of dimethylacrylic and β-methylcinnamic acids to lithium carboxylates of unsaturated carboxylic acids.

Structure and stereochemistry of melitensin, an elemanolide from Centaurea aspera var. stenophylla

Abstract A crystalline compound, melitensin, obtained from an extract of Centaurea aspera var. stenophylla was shown to be 8α, 15-dihydroxyelema- 1,3-6α, 12-dien-olide by X-ray analysis. The molecular structure of melitensin was solved with orthorhombic space group P 2 1 2 1 2 1 , a = 8.469(5) b = 10.769(5), c = 16.452(5)A for Z = 4 by direct methods and refined to a final R of 0.08 for 1493 observed reflections.

9α,15-Dihydroxygermacra-1(10),4-dien-11β,13-dihydro-6α,12-olide, a germacranolide isolated from Centaurea aspera subsp. stenophylla

Abstract A new germacranolide, isolated from Centaurea aspera subsp. stenophylla, was identified as 9β,15-dihydroxygermacra-1 (10)4-dien-11β,l3-dihydro-6α,12-olide by spectroscopic evidence and partial synthesis.

Polyenolates of Unsaturated Carboxylic Acids in Synthesis. Synthesis of Unsaturated α-Amino Acids and β-Hydrazing Acids

Abstract Regioselective reaction of lithium diene-and triene-diolates 1 and 2 with O-diphenylphosphinyl hydroxylamine affords unsaturated α-amino acids 3 and 4. Addition to DEAD leads selectively to γ-hydrazino unsaturated acids 5 and 6.