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201.
In this report, it is demonstrated that chiral vinyl aziridines can be stereospecifically ring expanded. This synthetic approach allows controlled access to chiral 2,5-cis- or 2,5-trans-3-pyrroline products from starting materials with the appropriate aziridine geometry. Twenty three ring expansion examples, most of which feature a stereospecific cyclization, are presented. 相似文献
202.
Larson SE Li G Rowland GB Junge D Huang R Woodcock HL Antilla JC 《Organic letters》2011,13(9):2188-2191
Conditions for a catalytic asymmetric aza-Darzens aziridine synthesis mediated by a vaulted biphenanthrol (VAPOL) magnesium phosphate salt is described. Using simple substrates, this methodology explores the scope and reactivity of a new magnesium catalyst for an aziridination reaction capable of building chirality and complexity simultaneously. 相似文献
203.
A Pd-catalyzed C4-olefination of oxazoles via C-H bond activation under mild conditions was achieved. The reaction was shown to be general over a range of substrates. New protocols for the divergent transformation of these products to provide functionalized amino alcohol and amino acid derivatives have also been established. 相似文献
204.
205.
In any Coxeter group, the conjugates of elements in the standard minimal generating set are called reflections, and the minimal
number of reflections needed to factor a particular element is called its reflection length. In this article we prove that
the reflection length function on an affine Coxeter group has a uniform upper bound. More precisely, we prove that the reflection
length function on an affine Coxeter group that naturally acts faithfully and cocompactly on ℝ
n
is bounded above by 2n, and we also show that this bound is optimal. Conjecturally, spherical and affine Coxeter groups are the only Coxeter groups
with a uniform bound on reflection length. 相似文献
206.
Milojevich CB Silverstein DW Jensen L Camden JP 《Journal of the American Chemical Society》2011,133(37):14590-14592
Experimentally measured resonance hyper-Raman (RHR) spectra spanning the S(1) ← S(0), S(2) ← S(0), and S(3) ← S(0) transitions in rhodamine 6G (R6G) have been recorded. These spectra are compared to the results of first-principles calculations of the RHR intensity that include both Franck-Condon (A-term) and non-Condon (B-term) scattering effects. Good agreement between the experimental and theoretical results is observed, demonstrating that first-principles calculations of hyper-Raman intensities are now possible for large molecules such as R6G. Such agreement indicates that RHR spectroscopy will now be a routine aid for probing multiphoton processes. This work further shows that optimization of molecular properties to enhance either A- or B-term scattering might yield molecules with significantly enhanced two-photon properties. 相似文献
207.
Seyedsayamdost MR Traxler MF Zheng SL Kolter R Clardy J 《Journal of the American Chemical Society》2011,133(30):11434-11437
Actinobacteria generate a large number of structurally diverse small molecules with potential therapeutic value. Genomic analyses of this productive group of bacteria show that their genetic potential to manufacture small molecules exceeds their observed ability by roughly an order of magnitude, and this revelation has prompted a number of studies to identify members of the unknown majority. As a potential window into this cryptic secondary metabolome, pairwise assays for developmental interactions within a set of 20 sequenced actinomycetes were carried out. These assays revealed that Amycolatopsis sp. AA4, a so-called "rare" actinomycete, produces a novel siderophore, amychelin, which alters the developmental processes of several neighboring streptomycetes. Using this phenotype as an assay, we isolated amychelin and solved its structure by NMR and MS methods coupled with an X-ray crystallographic analysis of its Fe-complex. The iron binding affinity of amychelin was determined using EDTA competition assays, and a biosynthetic cluster was identified and annotated to provide a tentative biosynthetic scheme for amychelin. 相似文献
208.
Copper-catalyzed cross-coupling reactions of amidine salts were utilized to synthesize monoarylated amidines in moderate to high yields with ligand-free conditions. DMF was the superior solvent for the N-arylation of benzamidines, while MeCN was used in the formation of N-aryl amidines in moderate to high yield. 相似文献
209.
210.