RESUMEN
Asymmetric hydroheteroarylation of alkenes represents a convenient entry to elaborated heterocyclic motifs. While chiral acids are known to mediate asymmetric addition of electron-rich heteroarenes to Michael acceptors, very few methods exploit transition metals to catalyze alkylation of heterocycles with olefins via a C-H activation, migratory insertion sequence. Herein, we describe the development of an asymmetric, intermolecular hydroheteroarylation reaction of α-substituted acrylates with benzoxazoles. The reaction provides 2-substitued benzoxazoles in moderate to excellent yields and good to excellent enantioselectivities. Notably, a series of mechanistic studies appears to contradict a pathway involving enantioselective protonation of a Rh(I)-enolate, despite the fact that such a mechanism is invoked almost unanimously in the related addition of aryl boronic acids to methacrylate derivatives. Evidence suggests instead that migratory insertion or beta-hydride elimination is enantiodetermining and that isomerization of a Rh(I)-enolate to a Rh(I)-heterobenzyl species insulates the resultant α-stereocenter from epimerization. A bulky ligand, CTH-(R)-Xylyl-P-Phos, is crucial for reactivity and enantioselectivity, as it likely discourages undesired ligation of benzoxazole substrates or intermediates to on- or off-cycle rhodium complexes and attenuates coordination-promoted product epimerization.
Asunto(s)
Acrilatos/química , Benzoxazoles/síntesis química , Compuestos Organometálicos/química , Fosfinas/química , Rodio/química , Benzoxazoles/química , Catálisis , Estructura Molecular , EstereoisomerismoRESUMEN
Cause and effect: In science, language is often subordinated to empirical data, but words can influence our ability to understand and communicate science. This Essay argues that imprecise language has confounded studies that probe the interactions underlying the anomeric effect and related phenomena.
RESUMEN
The number of elderly people with type 2 diabetes (T2D) is increasing worldwide. Community pharmacies, thanks to their proximity, provide more easy access to therapeutic education for rural patients. Populations living in isolated areas require specific educational resources related to their condition. The aim of this project was to perform a short (FLASH) educational intervention, coordinated by community pharmacists, and then evaluate the impact of this intervention on patient knowledge of their disease. The study was performed in Issoudun, a rural French town of approximately 10,000 inhabitants. Educational priorities were defined and the project was presented to health authorities and local health professionals. Pharmacies in Issoudun recruited patients, either alone or accompanied by their caregivers. The educational intervention lasted 2h and focused on 4 teaching objectives: knowledge concerning diabetes, diabetic complications and how to monitor them; how to react to hypoglycemia; understanding treatments; and understanding glycated hemoglobin. The impact of this educational intervention was assessed using a questionnaire delivered before the intervention, immediately after, and after 6months. Forty-five patients aged 71±6years with T2D duration of 14±6years were recruited over 6months. Some false beliefs were identified before the intervention. The educational session led to a significant improvement in the percentage of correct answers (before: 60.3%±7.5, after: 99%±0.4, P=0.0002) and at 6months (99.5%±0.3, P=0.0002) compared with the patients' initial knowledge. Almost all false beliefs were corrected by the intervention and patients were able to recall the mechanism of action of their drugs, with the help of a "key and lock" schematic. This short FLASH educational intervention, coordinated by community pharmacists, showed that the model was both interesting to patients and effective. This method could be expanded to other rural communities and medical deserts.
RESUMEN
We report the development of a multicatalytic, one-pot, asymmetric Michael/Stetter reaction between salicylaldehydes and electron-deficient alkynes. The cascade proceeds via amine-mediated Michael addition followed by an N-heterocyclic carbene-promoted intramolecular Stetter reaction. A variety of salicylaldehydes, doubly activated alkynes, and terminal, electrophilic allenes participate in a one-step or two-step protocol to give a variety of benzofuranone products in moderate to good yields and good to excellent enantioselectivities. The origin of enantioselectivity in the reaction is also explored; E/Z geometry of the reaction intermediate as well as the presence of catalytic amounts of catechol additive are found to influence reaction enantioselectivity.