Cyclic products can be obtained through the intramolecular version of the Nicholas reaction, which requires having the nucleophile connected to the alkyne unit. Here, we report the synthesis of ...1-oxa-3-cyclooctynes starting from commercially available (1
,3
)-camphoric acid. The strategy is based on the initial preparation of propargylic alcohols, complexation of the triple bond with Co
(CO)
, and treatment with BF
·Et
O to induce an intramolecular Nicholas reaction with the free hydroxyl group as nucleophile. Finally, oxidative deprotection of the alkyne afforded the cyclooctynes in good yields. Notably, large-sized R substituents at the chiral center connected to the O atom were oriented in such a way that steric interactions were minimized in the cyclization, allowing the formation of cyclooctynes exclusively with
configuration, in good agreement with theoretical predictions. Moreover, preliminary studies demonstrated that these cyclooctynes were reactive in the presence of azides yielding substituted triazoles.
The clinical use of virtual reality (VR) has proven its efficacy, especially when used as an exposure technique. A prominent property of VR's utility is its equivalence with the reality it ...represents. In this study, we explored this equivalence in a clinical context using neuroimaging. A sample of 32 adults with specific phobias (i.e., to cockroaches, spiders, or lizards) was divided into two groups: One was exposed to phobic stimuli using VR and the other was exposed to real phobic images (RI). We used brain activations as a dependent measure, focusing specifically on brain areas usually associated with fear processing. Whole-brain analysis detected higher activations for RI in the hippocampus, occipital, and calcarine areas. A specific analysis of the amygdala and insula also detected higher activations and extensions in response to RI, but VR stimuli also activated those areas in a significant manner. These results suggest that even in those cases where RI stimuli activate all of the brain's fear-processing circuits, VR stimuli do so as well. This implies that VR can be useful as an exposure technique similar to RI and applied as more than a mere training mechanism.
La importancia y utilidad de la síntesis asimétrica como una herramienta fundamental en la obtención de productos enantioméricamente puros o enriquecidos ha sido ampliamente reconocida por los ...químicos en campos tan diversos como la síntesis orgánica, la química médica, la química agrícola, la química de los productos naturales y la industria farmacéutica. Se desarrolla una versión asimétrica de la reacción de Nicholas, en la que se controla la estereoquímica del nuevo centro creado mediante la elección del apéndice propargílico adecuado y del nucleófilo apropiado, todo lo cual permite acceder a moléculas ópticamente activas a partir de precursores aquirales. Esta nueva metodología se aplica a la síntesis de 1,2-dioles, alfa-hidroxialdehídos y derivados de alfa-hidroxiácidos como enantiómeros puros. Estos estudios se extendieron para abarcar las ciclaciones producidas por ataque intramolecular de un grupo hidroxilo sobre el carbocatión generado por tratamiento ácido de complejos exo-(propargilo)Co2(CO)6. De este modo se sintetizaron sistemas de oxano-, oxepano- y oxocano-2.3-disustituidos de forma estereocontrolada y se extendió la metodología desarrollada a la síntesis de sistemas bicíclicos oxano-oxepano y oxepanos-2,7-disustituidos
Notas breves María Temes-Casas; Ángela Noguerol Seoane; Ana Rifon Lastra ...
Anales del Jardín Botánico de Madrid (1979),
12/2001, Letnik:
59, Številka:
2
Journal Article
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