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991.
We have recently developed a new type of chiral templates, dibenzosuberanes. Thess C2, symmetric diaryl modifiers have been successfully applied to the synthesis of chiral triarylcarbenium ions. They can serve as catalysts in the asymmetric Mukaiyama aldol reactions with moderate enantioselectivities of up to 50% [1]. We have subsequently found that one major side reaction between the catalyst and the substrate-silyl ketene acetal which releases extra silyl-X species is responsible for the erosion of asymmetric induction. The dibenzosuberane scaffold was found essential to prevent this type of side reaction. For the selection of carbenium counter ions, we have resorted to the chloride in order to completely suppress the undesired silyl catalysis [2]. 相似文献
992.
993.
994.
The intercalation of aluminosilicate clays proceeds via a critical conformation change. Ion exchange of the poly(oxypropylene)diamine salts allows widening of the clay layers from 12 Å to 20 Å and then a sharp increase to 58 Å. The data indicate a critical conformation change of the intercalated amines, thus providing a new way for manipulating nanomaterials and control of polymer conformations in layered silicate confinement.
995.
The Ramanujan Journal - Let F be a number field, and let $$F^{{\text {cyc}}}$$ be obtained by adjoining to F all the roots of unity. We show that as E ranges over all elliptic curves defined over... 相似文献
996.
997.
Chu-En Chou Yi-An Chen Yi-Ching Lin Shih-Chieh Kao Chieh-Yu Chang Yen-Ku Wu 《中国化学会会志》2020,67(12):2198-2203
Described is a formal synthesis of racemic schulzeines B and C that intercepts intermediates developed by Gurjar and co-workers. The synthetic sequence features an annulative coupling of a ketimine and acrylic acid enabling the construction of the benzoquinolizidine nucleus in a highly convergent manner. We also examined a continuous-flow version of the thermal aza-annulation, which proved less practical as compared to the batch processes. 相似文献
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999.
During the course of investigating the anticancer activities of new compounds, we have synthesized a series of novel cyclic N-hydroxyurea derivatives and several carbamate intermediates1–3. Infrared absorption, nuclear magnetic resonance, and electronic absorption spectra were examined in order to confirm the identities and to study the molecular structure of these compounds. 相似文献
1000.