Alice Gateau-Olesker

3-Alkyl 1,6-dihydropyridines from 3-alkyl 5,6-dihydro-pyridinium salts. Implications in the biosynthesis of some macrocyclic marine alkaloids

Abstract Additions of salts 1 and dihydropyridines 2 in an intramolecular manner have been invoked in the biosynthesis of some macrocyclic alkaloids such as manzamines, sarain A and halicyclamine A, recently isolated from sponges. We report conditions for the deprotonation of easily accessible salts 1 , giving a regioselective entry to 3-alkyl 1,6-dihydropyridines 2 . Also, we show that species 1 and 2 can be generated from a common intermediate such as 9 . Dihydropyridines 2 are unstable at high temperatures giving isomeric 1,2- and 1,4-dihydropyridines, but were conveniently trapped by dienophiles to give synthetically useful isoquinuclidines such as 18 or 20 .

Synthesis of macrocyclic or linear pyridinium oligomers from 3-substituted pyridines. Model synthetic studies toward macrocyclic marine alkaloids

Abstract Refluxing of 3-substituted pyridine 6 in acetonitrile resulted in the formation of a series of oligomers 8 , which with an average value of n=14, were found to possess cytotoxicity comparable with those of natural toxins 1 extracted from sponges. By contrast, refluxing of 6 in the presence of potassium iodide afforded the bispyridinium macrocycle 7 in fairly good yield. The macrocyclic compound 7 , whose structure was established by X-ray analysis, afforded in four steps an intermediate 13 which proved to be a stable precursor of bis 5,6-dihydropyridinium salt 12 or unstable bis 1,6-dihydropyridine 14 . These compounds are expected to be suitable models for studying intramolecular additions of species 4 which are considered to be key intermediates in the biosynthesis of a number of recently discovered macrocyclic pyridine alkaloids.

Asymmetric synthesis of 1,3,4-trisubstituted and 3,4-disubstituted 2-azetidinones: strategy based on use of D-glucosamine as a chiral auxiliary in the Staudinger reaction

An efficient asymmetric approach to the synthesis of trisubstituted azetidin-2-ones is presented. The strategy relies on the use of ketene–imine cycloaddition between ketenes generated from phthalimidoacetic and methoxyacetic acids and a chiral Schiff base (3) derived from 3,4;5,6-di-O-isopropylidene-D-glucosamine propane dithioacetal (2) and cinnamaldehyde; the removal of the chiral auxiliary group by β-elimination is a noteworthy facet of this communication.

Chiral synthesis of 3,4-disubstituted 2-azetidinones from (R,R)-(+)-tartaric acid

Abstract A novel route Is described for the enantioselective synthesis of 2-azetidinones 24 and 25 from (R,R)-(+)-tartaric acid. Monomethylation, monobenzylation of 2 and the use of site specific pig liver esterase (PLE) to produce 6 and 7 are the key steps in the sequence.

Radical decarboxylative alkylation of tartaric acid

Abstract New derivatives of L-(+)-tartaric acid have been synthesized from the monomethyl-2,3-O-isopropylidene (R,R)-(+)-tartrate by visible light photolysis of its N-hydroxy-2-thiopyridone ester derivative in presence of activated alkenes. The carbon radical generated at the dioxolane ring adds stereoselectively to olefins to give the addition products with retention of configuration.

Stereospecificity in radical carbon–carbon bond formation reactions based on tartaric acid

Radical decarboxylative addition to activated alkenes, using the thiohydroxamic ester method, of a suitably protected derivative of (+)-L-tartaric acid leads to overall substitution of the carboxy group with essentially complete retention of configuration.

Synthesis of trans-(3S,4S)-dibenzyloxycyclopentanone

The 1-cyano-1-thiophenylcyclopentone derivative 1, obtained from (R,R)-(+)-tartaric acid, has been converted into a number of derivatives including the important trans-(3S,4S)-dibenzyloxycyclopentanone 2 in 45% overall yield.

Synthese de sucres a chaine allongee heptose et octose par c-acylation nucleophile

Abstract The synthesis of extended chain; heptoses and octoses was achieved by nucleophilic C-acylation using carbanions derived from 1,3-dithiane 1 and 2-methyl-1,3-dithiane 10 on 1,2:3,4-di-O-isopropylidene-α- d -galacto-1, 5-hexodialdopyranose 2 . The diastereoisomeric products 3 and 4 or 11 and 12 are formed in different proportion according to the solvent used. 11 was transformed by azidolysis into dithiepane derivatives 14 , 15 and 16 . From the intermediate 12 , the diol 18 , a precursor of lincosamine, was obtained.

Novel (4 + 1) fragment combination approach to chiral cyclopentanoids from tartaric acid

A chiral cyclopentanoid building block 29 has been synthesized in “one pot” cyclization process from epoxides 22 - 25 (which are readily accessible from (R,R)-(+) tartaric acid) with the carbanion derived from phenylthioacetonitrile (PhS-CH2-CN).

Synthèse d'analogues de dérivés dioxaprostanoïques à partir du d et du l-xylose

Abstract Epoxides 7 , 8 and 9 have been prepared from d and l -xylose, and used for the synthesis of a precursor of ent -(11-oxa)PG 19 and of 9,13-and 7,11-dioxaprostanoic acids 28 and 31 . The site of the opening of the epoxidcs 7 and 9 with the carbanion derived from bis -(phenylth)romethane and with LiAlH 4 is shown by establishing structures of the products 11 , 12 , 20 et 21 by 13 CNMR spectroscopy.