31 research outputs found
Ions sulfénates et catalyse (une voie alternative aux sulfoxydes)
No full textLes anions sulfénates, nucléophiles soufrés hautement réactifs de formule générale RSO , sont des espèces particulièrement attractives pour la synthèse de sulfoxydes. Toutefois, ce potentiel n est exploité que depuis peu de temps. Les travaux entrepris s inscrivent dans ce contexte et ont pour point commun des conditions de catalyse. Dans un premier temps, l utilisation d un agent de transfert de phase énantiopur dérivé du quinquina (organocatalyse) en présence d un halogénoalcane a permis d accéder à des sulfoxydes énantioenrichis. Des aryl alkyl sulfoxydes ont ainsi été préparés avec de bons rendements chimiques compris entre 63 et 96%, et des excès énantiomériques jusqu à 58%. Concernant les dérivés dialkyles, les rendements sont plus faibles, compris entre 34 et 52%, mais les excès énantiomériques restent corrects et peuvent atteindre 47%. Les sulfénates sont générés in situ par une réaction de rétro-Michael à partir de sulfinyl sulfones. Dans un deuxième temps, des sulfoxydes diaromatiques ont été obtenus par une réaction d arylation dans des conditions de catalyse organométallique. Nous avons ainsi développé une méthode de génération inédite de sulfénates par décomposition thermique de sulfoxydes de tert-butyle en milieu basique et mis au point un système catalytique au palladium efficace. Un nouvel équivalent synthétique de SO2-, le sulfoxyde de di-tert-butyle, a été exploité dans des réactions de double arylation. Finalement, des versions diastéréosélectives du couplage ont été abordées avec l emploi de structures comportant un motif [2.2]paracyclophane (chiralité plane) ou biarylique (chiralité axiale).Sulfenate salts are highly reactive sulfur nucleophiles, which possess the general structure RSO-. They are very attractive precursors of sulfoxides, by way of S-C bond formation, as exemplified with recent contributions to the literature. The present work focussed on catalytic functionalization of sulfenates. First of all, enantioenriched sulfoxides were prepared using a Cinchona phase-transfer reagent in the presence of an alkyl halide. Aryl alkyl sulfoxides were prepared with high chemical yields in the range of 63 and 96%, and in up to 58% ee. Lower yields were obtained for dialkyl compounds (34-52%), but the enantioselectivity was still acceptable (up to 47% ee). Sulfenate species were generated in situ from sulfinyl sulfones according to a retro-Michael reaction. Then, diaryl sulfoxides were prepared using a transition metal-catalyzed arylation reaction. A novel approach to sulfenates, based on the thermal fragmentation of tert-butyl sulfoxides under basic conditions, has been exploited. An efficient palladium catalytic system has also been developed. The methodology was extended to a double arylation reaction, which involves di-tert-butyl sulfoxide, a synthetic equivalent of SO2- species. Finally, diastereoselective versions of the coupling have been examined through planar chiral [2.2]paracyclophane and chiral axial biaryl structures.CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF
The phosphorus-Claisen condensation
No full textInternational audience1,1-Bisphosphorus compounds are easily synthesized through the phosphorus-Claisen (phospha-Claisen) condensation between a phosphorus-stabilized anion and a phosphorus electrophile. The preliminary scope of this reaction is investigated in terms of employable phosphorus reagents. Valuable intermediates are conveniently prepared in a single step. Overall, the method is competitive with multistep procedures which require the preparation of PCl intermediates derived from the P(OR) reagents we instead employ directly, and it delivers complex organophosphorus compounds in moderate to good isolated yields. An example of the intramolecular version of the reaction, the phospha-Dieckmann condensation, is also reported
Chiral nonracemic sulfoxides by asymmetric alkylation of alkanesulfenates in the pPresence of a chiral ammonium phase transfer catalyst derived from Cinchona alkaloid
No full textInternational audienc
ChemInform Abstract: Manganese‐Catalyzed and Promoted Reactions of H‐Phosphinate Esters.
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ChemInform Abstract: tert‐Butyl Sulfoxides: Key Precursors for Palladium‐Catalyzed Arylation of Sulfenate Salts.
No full texttert -Butyl Sulfoxides: Key Precursors for Palladium-Catalyzed Arylation of Sulfenate Salts
No full textInternational audienceThe present report describes an efficient and clean generation of sulfenate salts (R1SO−) by pyrolysis of readily available tert‐butyl sulfoxides to give sulfenic acids (R1SOH) and traceless isobutene, followed by hydrogen abstraction with a weak inorganic base (K3PO4). The relevance of this process was exemplified through an in situ palladium‐catalyzed cross‐coupling reaction with aryl halides/triflates leading to aryl sulfoxides. The operationally simple CS bond‐forming protocol developed uses Pd(dba)2 as catalyst and Xantphos as ligand in toluene or a toluene/H2O mixture. Further extensions include the use of di‐tert‐butyl sulfoxide as an equivalent for sulfur monoxide dianion (SO2−) and the development of diastereoselective versions in the [2.2]paracyclophane and biaryl series
Trifluoromethylthiolation of -Chloroaldehydes: Access to Quaternary SCF3-Containing Centers
No full textIn this study, a straightforward methodology was developed to access quaternary -trifluoromethylthiolated chloroaldehydes. Using the Munavalli reagent as the electrophilic SCF3 source, a base-catalyzed trifluoromethylthiolation reaction with a panel of -chloroaldehydes was successfully achieved under mild reaction conditions. The -trifluoromethylthiolated chloroaldehydes were obtained in moderate to high yields (up to 88%). This approach demonstrated a good functional-group tolerance and offered access to highly functionalized quaternary trifluoromethylthiolated aldehydes, inaccessible so far. The development of an enantioselective version was investigated by using a chiral phase-transfer catalyst, giving the enantioenriched product in moderate enantiomeric excess
UV-mediated hydrophosphinylation of unactivated alkenes with phosphinates under batch and flow conditions
No full textIn this study, we report an efficient UV-mediated hydrophosphinylation of unactivated alkenes with H-phosphinates and hypophosphorous acid under radical free conditions in batch and in continuous flow.</p
