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The naturally occurring sesquiterpene sorgolactone (2) belongs to the class of “strigolactones”, which are highly potent germination stimulants for seeds of the parasitic weeds Striga and Orobanche. The aim of the present work was to synthesize all eight stereoisomers of sorgolactone and to evaluate their activities in the stimulation of germination of S. hermontica and O. crenata. Two racemic diastereomers of the ABC part of sorgolactone, rac.10a and rac.10b respectively, were prepared and coupled with homochiral latent D-ring synthons 12 and ent.12. In this manner, four mixtures of two separable (protected) sorgolactone diastereomers were obtained. Deprotection gave all eight target compounds as single isomers. Bioassays revealed that only those isomers possessing the same stereochemistry as natural sorgolactone at two adjacent chiral centers exhibit high biological activities.

Racemic 5-hydroxy-4-oxa-endo-tricyclo[5.2.1.0(2,6)]dec-8-en-3-one and its 2-methyl analogue were resolved employing a lipase-catalyzed acetylation reaction. The latter compound thus gave access to a homochiral D-ring synthon for strigolactones. The enzymatic acetylation reaction occurred with a remarkable inversion of configuration at C-5, through which it is possible to achieve a highly efficient asymmetric synthesis of 5-acetoxy-2(5H)-furanone.

The stereospecific total synthesis of the naturally occurring macrolide patulolide C 19Eb as well as its iso, nor, and homo analogs is described by applying the photoinduced rearrangement of enantiomerically pure epoxy diazomethyl ketones 14 to γ-hydroxy α,β-unsaturated esters 15 as the key step. The required epoxy diazomethyl ketones 14 are obtained by a Sharpless epoxidation of an appropriate allylic alcohol, followed by ruthenium tetraoxide oxidation to an oxiranecarboxylic acid, conversion into a mixed anhydride, and treatment with diazomethane. Macrolide 19Zb, which is a geometrical isomer of 19Eb, turned out to be a diastereomer of natural macrolide isopatulolide C, which implies the 4R,11R configuration for this natural material. X-ray diffraction analyses of 19Ea and 19Eb show that there is a considerable difference in spatial arrangement; particularly, the different torsion angles between the carbonyl and olefinic bonds are noteworthy. The conformational behavior of these macrolides is also deduced from the NMR and UV spectra

An efficient synthesis of both (1S,4R) and (1R,4S)-4-N-acetylamino-1-benzoylcyclopent-2-enes 33 has been accomplished starting from enantiopure 5-(1'-phenylethylamino)-endo-tricyclo[5.2.1.0(2,6)]deca-4,8-dien-3-ones 14 and 15. N-Acetylation of both 15 and 14 followed by single electron-transfer reduction using lithium in liquid ammonia afforded diastereomeric mixtures of beta-amino ketones 26 and 27 and of ent-26 and ent-27 in high yields and with high diastereoselectivity. In this reduction process, the enaminone double bond is reduced with the concomitant removal of the alpha-methylbenzyl group as the chiral auxiliary. Thermolysis of the respective diastereomic mixtures of 26 and 27 in the gas phase (FVT) or in solution afforded 4-N-acetylaminocyclopent-2-ene-1-ones 30 in high optical and chemical yields. Acidic hydrolysis of (+)-30 gave (R)-(+)-4-aminocyclopentenone 31 as its hydrochloride. Stereoselective reduction of 30 using sodium borohydride and cerium chloride heptahydrate furnished amido alcohol 32, which was isolated and characterized as its benzoyl derivative 33.

Lucidene (1), a bis(benzopyranyl) sesquiterpene was isolated from the rootbark of Uvaria lucida ssp. lucida, and its structure was determined by spectroscopic methods and single-crystal X-ray crystallography. It is optically inactive and crystallizes in enantiomeric pairs. High-resolution 1H NMR (400 and 600 MHz) spectroscopy allowed the assignment of all protons and indicated the existence of relatively slowly interconverting conformations. The three known dihydrochalcones, uvaretin, diuvaretin, and chamuvaretin, as well as benzyl benzoate were isolated from the same plant as well.

Synthese d'α-sulfinyl-cetones et esters(I). Cycloaddition du dimethyl-2,3 butadiene-1,3 avec (I) conduisant a des oxydes-1 d'(alcoxycarbonyl-2 (ou aroyl) dihydro-3,4) thiopyranne

Synthese de S-imides de thiones soit par reaction de N-sulfinyl arylamines avec le trimethylsilyl-fluorenure ou -xanthenure, soit par addition d'(aryl trimethylsilyl) amidures sur des S-oxydes de thiones

Les azides d'acides oxirannecarboxyliques sont obtenus a partir des esters; etude de leur transposition de Curtius