RESUMEN
We successfully expand the application of lactols or cyclic hemiaminals as nucleophiles for the asymmetric synthesis of both N,O- and N,N-acetal moieties contained in the structure of ring-fused piperidine derivatives. This efficient one-pot protocol involves an organocatalyzed asymmetric aza-Diels-Alder reaction and iminium ion induced cyclization sequence to ultimately deliver heterocyclic compounds with excellent stereoselectivity in high yield, containing three continuous stereogenic centers.
RESUMEN
In order to optimize extraction process conditions of tannins from Geranium orientali-tibeticum by supercritical CO2, the content of tannins was determined by phosphomolybdium tungsten acid-casein reaction, with extraction pressure, extraction temper- ature and extraction time as factors, the content of tannins from extract of G. orientali-tibeticum as index, technology conditions were optimized by orthogonal test. Optimum technology conditions were as follows: extraction pressure was 25 MPa, extraction temperature was 50 °C, extracted 1.5 h. The content of tannins in extract was 12.91 mg x g(-1), extract rate was 3.67%. The method established could be used for assay the contents of tannin in G. orientali-tibeticum. The circulated extraction was an effective extraction process that was stable and feasible, and that provides a way of the extraction process conditions of tannin from G. orientali-tibeticum.
Asunto(s)
Dióxido de Carbono/química , Fraccionamiento Químico/métodos , Geranium/química , Taninos/aislamiento & purificación , Medicamentos Herbarios Chinos/químicaRESUMEN
An open-close strategy in asymmetric catalysis is newly developed. With this powerful strategy, lactols are directly applied as potential precursors of lactones in enamine-based asymmetric Michael reactions providing a facile access to α-functionalized lactones containing two adjacent stereogenic centers as a single diastereomer in good to excellent yields (up to 99%) and with excellent enantioselectivities (most cases >99%). Moreover, the reaction products are shown to give highly functionalized derivatives by stepwise systematic transformations.