Synthèse partielle de la (20S)-ψ-vincamine et de la (20S)-épi-16ψ-vincamine

Partial Synthesis of (20S)-ψ-Vincamine and (20S)-epi-16ψVincamine An attempt of classification of the indole alkaloids is presented; (20S)-ψ-vincamine. (20S)-16-épi-ψ-vincamine and (20S)-ψ-apo-vincamine have been prepared from catharanthine by partial synthesis.     

Synthèse de la diméthyl-4,4-dihydrofuranedione-2,3

4,4-Dimethyl-dihydro-2,3-furanedione ( 4 ), an intermediate in the synthesis of (+)-D -pantothenic acid, is obtained in good yield from readily available substances such as isopropyl chloride, diethyl oxalate and formaldehyde, without oxidative conditions.     

Synthèse des (R)- et (S)-O-isopropylidène-1,2-glycérols. Détermination de la pureté optique

Synthesis of the (R)- and (S)-Glycerol Acetonides. Determination of the Optical Purity The optical purity of (R)-glycerol acetonide ( 1 ) and (S)-glycerol acetonide ( 1 ′) has been determined with great accuracy by gas chromatography after derivatization. The optical purity of (S)-glycerol actonide prepared from D -mannitol was > 99.4% while for (R)-glycerol acetonide obtained from L -serine it was 95%.     

Synthèse d'amino-oxadiazoles - 1, 2, 4

Two new syntheses of 5-amino-1,2,4-oxadiazoles are described. The first one is based on the reaction of guanidine on benzhydroxamyl chloride. The second is more general and consists in allowing primary or secondary amines, hydrazine or guanidine to react with 5-trichloromethyloxadiazoles.     

Synthèse de céphalosporine-lactones

Condensation of azetidinones 2a and 2b with mercaptan 3 gave respectively compound 10 or a 1:1 mixture of 17 and 17 ′. Bromination of 10 , afforded cis and trans-bromohydrins 13a and of 17 and 17 ′ cis and trans-bromohydrins 18a . Acetylation and reduction with zinc and acetic acid of these bromohydrins gave cephems 4a or 4b and 4b ′ respectively.     

Synthèse et transformations de pyridopyrimidopyrimidines

A convenient one-step synthesis of a pyridoprimidopyrimidine system by means of the chloride of 1,3-dimethy1-4amino-5-amino-5-(N,N-dimethyliminiumchloromethine)uracil and substituted pyridines is studied and the title compounds are described.     

Synthèse de N-2 alkyl (aryl) dioxo-3,5 oxadiazolidine-1,2,4

The synthesis of new 3,5 dioxo-1,2,4 oxadiazolidines whixh are N-2 substituted bioisosters of biologically active carboxylic compounds was studies. Nitro compounds were used as starting materials, and triton B as the cyclizing base. The expected N-2 allyl and aryl substituted derivatives were obtained in satisfactory yields.     

Synthèse de l'évernine

Synthesis of Evernin Two syntheses of the depside evernin 6 are described. Condensation of methyl acetoacetate and methyl crotonate followed by aromatization and reduction with Raney-Ni led to methyl orsellinate (3) . The condensation of everninic acid (4) , obtained by partial methylation of 3 and saponification of the methyl ester, with methyl 2, 4-dihydroxy-3, 6-dimethylbenzoate (methyl β-orcin carboxylate) (5) in presence of cyclohexylcarbodiimide gave evernin ( 6 ). In a second syntheis methyl dihydroorsellinate (1) was regiospecifically converted into its 4-methyl enol ether and aromatized via the benzene selenenyl derivative to yield methyl evernate (7) . Benzylation followed by saponification gave the free acid 8 . Methyl β-orcin carboxylate (5) was synthesized in an analogous way from methyl 3,6-dimethyl-2,4-dioxocyclohexanecarboxylate. Condensation of 8 with the methyl ester 5 by treatment with trifluoroacetic anhydride in toluene yielded 9 , which could be converted into evernin ( 6 ) by hydrogenolysis of the benzyl ether.     

Synthèse de l'ériodermine

Synthesis of Eriodermin The total synthesis of eriodermin (=2,7-dichloro-4-formyl 3-hydroxy-8-methoxy-1,6-dimethyl-11H-dibenzo[b,e] [1,4]dioxepin-11-one) is described.     

Synthèse et structure de benzopyranno-1 triazines-1,2,4

Under basic conditions 2,2,6-trimethyl-3,4-chromanedione is cy8clised nto I-benzopyranno[4,3-e]triazin-3-one. In acetic meduum, semicarbazide hydrochloride and diketone provide the I-benzopyranno[4,3-e] and [3,4-e]triazin-3-ones. However, under the same conditions, the thiosemi-carbazide leads exclusively to the I-benzopyranno[4,3-e]triazine-3-thione. The structure of these compounds is in agreement with the ¹³C nmr spectra.     

Stereochemische Korrelationen zwischen (2R,4′R,8′R)-α-Tocopherol, (25S,26)-Dihydroxycholecalciferol, (–)-(1S,5R)-Frontalin und (–)-(R)-Linalol

Stereochemical Correlations between (2R,4′R,8′R)-α-Tocopherol, (25S,26)-Dihydroxycholecalciferol, (–)-(1S,5R)-Frontalin and (–)-(R)-Linalol The optically active C₅- and C₄-building units 1 and 2 with their hydroxy group at a asymmetric C-atom were transformed to (–)-(1S,5R)-Frontalin ( 7 ) and (–)-(3R)-Linalol ( 8 ) respectively; 1 and 2 had been used earlier in the preparation of the chroman part of (2R,4′R,8′R)-α-Tocopherol ( 6a , vitamin E), and for introduction of the side chain in (25S,26)-Dihydroxycholecalciferol ((25S)- 4 ), a natural metabolite of Vitamin D₃. The stereochemical correlations resulting from these converions fit into a coherent picture with those correlations already known from literature and they confirm our earlier stereochemical assignments. A stereochemical assignment concerning the C(25)-epimers of 25,26-Dihydroxycholecalciferol that was in contrast to our findings and that initiated the conversion of 1 and 2 to 7 resp. 8 for additional stereochemical correlations has been corrected in the meantime by the authors [26].     

Synthèse de l'acide décarboxythamnolique

Synthesis of Decarboxythamnolic Acid The total synthesis of the meta-depside decarboxythamnolic ( = 3-[(3-formyl-2-4-dihydroxy-6-methyl-phenyl)oxy]-2-hydroxy-6-methoxy-4-methylbenzoic acid; 25 ) by the biomimetic condensation of the substituted β-orcinol units 9 and 22 is described.     

Synthèse de dérivés de la benzo[c] quinolizine

The introduction of polar groups in planar polycyclic systems, for the purpose of studying their intercalating action, has been realized in the benzo[c]quinolizinium series. A functionalizing synthesis has been developed from 2-picolyl-and quinaldyllithium. Intermediate ketones or imines were cyclized by a quaternization reaction involving a concerted process. Structure and physico-chemical features of the compounds prepared were studied.     

Synthèse de quelques alcoxy-2 et aryloxy-2 dioxolannes-1,3

2-Methoxy, 2-ethoxy, and 2,2-diethoxy-1,3-dioxolanes, substituted in the 4,5 and in the 2 position by methyl or phenyl groups were obtained by an uncatalyzed reaction between a vicinal diol and an orthoester. An acid catalyst (p-toluene sulfonic acid) was necessary in order to obtain the 2-phenyl-2-methoxydioxolanes. 2-Phenoxydioxolanes were prepared by an exchange reaction between phenol and the corresponding 2-ethoxydioxolane.     

Synthèse de 2-pyrimidinylphénols et de 2-pyrazolylphénols

New pyrimidynylphenols 9a-e and pyrazolylphenols 10a-e substituted with an aminomethl moiety are described. These compounds were prepared in good yields by use of guanidine corbonate and hydrazine hydrate on the aminomethylchromones 8a-e . Aminomethylchromones were readily obtained via the Mannich reaction on chromone 5 . Optimized yields of chromone 5 and 3-aminomethylchromones 8a-e are reported.