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621.
622.
Karl Kratzl 《Mikrochimica acta》1956,44(1-3):159-170
Ohne Zusammenfassung 相似文献
623.
Kathrin Bringmann 《The Ramanujan Journal》2006,12(2):257-266
We use Rademacher’s method to obtain asymptotic expressions for some restricted partition functions. For fixed positive integers
m > 1 and l, we consider the number p
m
(n) of partitions of n into summands not divisible by m, and the number p
m
l
(n) of partitons of n with the further restriction that any integer occurs at most l times as a summand.
2000 Mathematics Subject Classification Primary—11P82; Secondary—11P83 相似文献
624.
P. Claus E. Klein W. Grosch H. Bertl K. Kratzl 《Monatshefte für Chemie / Chemical Monthly》1966,97(1):271-280
Zusammenfassung Es wird die Synthese von N-Hydroxymethylamiden choleretisch wirksamer Phenolcarbonsäuren sowie von Alkoxymethyläthern mykostatisch wirksamer Phenolcarbonsäureester beschrieben.
Meinem Lehrer, Herrn Prof.A. v. Wacek, zum 70. Geburtstag gewidmet. 相似文献
The preparation of N-hydroxymethylamides of phenolic carboxylic acids with choleretic activity and of alkoxymethyl ethers of phenolic ethyl benzoates with mycostatic activity is described.
Meinem Lehrer, Herrn Prof.A. v. Wacek, zum 70. Geburtstag gewidmet. 相似文献
625.
Carina Onneken Kathrin Bussmann Ryan Gilmour 《Angewandte Chemie (International ed. in English)》2020,59(1):330-334
Enantiodivergent, catalytic reduction of activated alkenes relays stereochemical information encoded in the antipodal chiral catalysts to the pro‐chiral substrate. Although powerful, the strategy remains vulnerable to costs and availability of sourcing both catalyst enantiomers. Herein, a stereodivergent hydrogenation of α,β‐unsaturated phosphonates is disclosed using a single enantiomer of the catalyst. This enables generation of the R‐ or S‐configured β‐chiral phosphonate with equal and opposite selectivity. Enantiodivergence is regulated at the substrate level through the development of a facile E → Z isomerisation. This has been enabled for the first time by selective energy transfer catalysis using anthracene as an inexpensive organic photosensitiser. Synthetically valuable in its own right, this process enables subsequent RhI‐mediated stereospecific hydrogenation to generate both enantiomers of the product using only the S‐catalyst (up to 99:1 and 3:97 e.r.). This strategy out‐competes the selectivities observed with the E‐substrate and the R‐catalyst. 相似文献
626.
Dr. Ashot Gevorgyan Prof. Dr. Kathrin H. Hopmann Prof. Dr. Annette Bayer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(27):6064-6069
A formal C−H carboxylation of unactivated arenes using CO2 in green solvents is described. The present strategy combines a sterically controlled Ir-catalyzed C−H borylation followed by a Cu-catalyzed carboxylation of the in situ generated organoboronates. The reaction is highly regioselective for the C−H carboxylation of 1,3-disubstituted and 1,2,3-trisubstituted benzenes, 1,2- or 1,4-symmetrically substituted benzenes, fluorinated benzenes and different heterocycles. The developed methodology was applied to the late-stage C−H carboxylation of commercial drugs and ligands. 相似文献
627.
Lackner G Schenk A Xu Z Reinhardt K Yunt ZS Piel J Hertweck C 《Journal of the American Chemical Society》2007,129(30):9306-9312
The benastatins, pradimicins, fredericamycins, and members of the griseorhodin/rubromycin family represent a structurally and functionally diverse group of long-chain polyphenols from actinomycetes. Comparison of their biosynthetic gene clusters (ben, prm, fdm, grh, rub) revealed that all loci harbor genes coding for a similar, yet uncharacterized, type of ketoreductases. In a phylogenetic survey of representative KRs involved in type II PKS systems, we found that it is generally possible to deduce the KR regiospecificity (C-9, C-15, C17) from the amino acid sequence and thus to predict the nature of the aromatic polyketide (e.g., angucycline, anthracycline, benzoisochromanequinones). We hypothezised that the new clade of KRs is characteristic for biosynthesis of polyphenols with an extended angular architecture we termed "pentangular". To test this hypothesis, we demonstrated the biogenetic relationship between benastatin and the structurally unrelated spiro ketal griseorhodin by generating a mutant producing collinone, a pentangular pathway intermediate. The benastatin pathway served as a model to characterize the KR. Gene inactivation of benL resulted in the formation of a series of 19-hydroxy benastatin and bequinostatin derivatives (e.g., benastatin K and benastatin L). These results clearly showed that BenL functions as a C-19 KR in pentangular pathways. 相似文献
628.
Inzenhofer K Schmalz T Wrackmeyer B Motz G 《Dalton transactions (Cambridge, England : 2003)》2011,40(17):4741-4745
Polymer derived ceramics have received lots of attention throughout the last few decades. Unfortunately, only a few precursor systems have been developed, focusing on silicon based polymers and ceramics, respectively. Herein, the synthesis of novel hafnium containing organometallic polymers by two different approaches is reported. Dialkenyl substituted hafnocene monomers were synthesized and subsequently polymerized via a free radical mechanism. Salt metathesis reactions of hafnocene dichloride with bifunctional linkers led to the formation of polymeric materials. NMR spectroscopic methods--in solution as well as in the solid state--were used to characterize the organometallic polymers. Ceramics were finally obtained after cross-linking and thermal treatment under argon (T(max) = 1800 °C). SEM investigations, elemental analyses, Raman spectroscopy and XRD investigations identified the pyrolyzed products as partially crystalline HfC/C mixed phases. 相似文献
629.
Addis D Das S Junge K Beller M 《Angewandte Chemie (International ed. in English)》2011,50(27):6004-6011
In the last decade, an increasing number of useful catalytic reductions of carboxylic acid derivatives with hydrosilanes have been developed. Notably, the combination of an appropriate silane and catalyst enables unprecedented chemoselectivity that is not possible with traditional organometallic hydrides or hydrogenation catalysts. For example, amides and esters can be reduced preferentially in the presence of ketones or even aldehydes. We believe that catalytic hydrosilylations will be used more often in the future in challenging organic syntheses, as the reaction procedures are straightforward, and the reactivity of the silane can be fine-tuned. So far, the synthetic potential of these processes has clearly been underestimated. They even hold promise for industrial applications, as inexpensive and readily available silanes, such as polymethylhydrosiloxane, offer useful possibilities on a larger scale. 相似文献
630.
Jagadeesh RV Wienhöfer G Westerhaus FA Surkus AE Pohl MM Junge H Junge K Beller M 《Chemical communications (Cambridge, England)》2011,47(39):10972-10974
Pyrolysis of iron-phenanthroline complexes supported on carbon leads to highly selective catalysts for the reduction of structurally diverse nitroarenes to anilines in 90-99% yields. Excellent chemoselectivity for the nitro group reduction is demonstrated. 相似文献