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Showing 1 to 20 of 111 for “"Ring System"”.
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Dusty ringlets in Saturn’s ring system
Recently, several faint ringlets in the Saturnian ring system were found to maintain a peculiar orientation relative to Sun. The Encke gap ringlets as well as the ringlet in the outer rift of the Cassini division were found to have distinct spatial displacements of several tens of kilometers away …
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Synthesis of the Ophiobolin Ring System
… has been extended to a synthesis of a 5-8-5 ring system having the relative configuration of the ophiobolin and ceroplastol sesterterpenes. The relative stereochemistry of three of the four asymmetric centers was determined by x-ray crystallographic analysis of an intermediate iodide. …
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Approaches to the Synthesis of the Ophiobolin Ring System
… provides a novel method for effecting two-carbon ring expansion.
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The preparation of polynuclear compounds containing the thiophene ring system
The process of C. K. Bradsher for preparing mesosubstituted anthracene and 1,2-benzanthracene derivatives has been widely extended. The purpose of this research was to extend this process to the thiophene series, in addition to continuing some work on the 9-(dimethyl)- phenylanthracene series and …
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An investigation of the structure and dynamics of the Uranian ring system
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1989.
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A Photochemical Approach to the a-B Ring System of the Ophiobolin Sesterterpenes
Made available in DSpace on 2014-12-13T20:10:46Z (GMT). No. of bitstreams: 1 8008965.pdf: 4772289 bytes, checksum: ce635ac7eedc2579b3b51e8fe2ec472b (MD5) Previous issue date: 1979
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Total Synthesis of Lasionectrin and Synthetic Studies Towards Pestaloxazine A
… which contains a fused pyrone-tetrahydrofuran ring system. Several synthetic strategies were explored to prepare the carbon skeleton of lasionectrin (13). Our initial approach which hinged on formation of the fused bicycle in a single step using chiral hypervalent iodine was ultimately …
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Total synthesis of Class II and Class III Galbulimima Alkaloids
… reaction provided the required trans-decalin AB-ring system and masked the Cl 6-carbonyl as an N-vinyl carbamate for late stage unveiling in the form of the necessary C16-enone. A vinyl-radical cyclization secured the C-ring while successful execution of our strategy for introduction of the …
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1. Chromium(0)- Promoted Higher Order Cycloaddition Reactions: Studies Toward The Total Synthesis Of The Cyclocitrinols And Echinopines A And B 2. Total Synthesis Of (±)-Debromoflustramine B Via [4+1] Cyclization Of An Indole Isocyanate And A Bis(alkylthio)carbene
… The key structural unit, the bicyclo[4.4.1]A/B ring system, was constructed by a regioselective Cr(0)-promoted [6π + 4π] photochemical cycloaddition reaction.</p> <p>A Bronsted acid catalyzed rearrangement of the 11-trimethylsilyl-tetracyclo[8.1.0.03,7.04,11]undeca-5,8-diene ring system to the …
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Total synthesis of Galbulimima alkaloids. Resin-bound glycosyl phosphates as glycosyl donors.
… reaction provided the required trans-decalin AB ring system and masked the C16-carbonyl as an N-vinyl carbamate for late stage oxidative unveiling as the corresponding C16-enone. Completely diastereoselective introduction of the C-ring via radical cyclization chemistry followed by an …
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Carbomagnesium mediated reactions: A versatile tool in organic synthesis.
… reactions. An expedient route to the Taxol A/B-ring system (329) was developed. This ring system underwent a facile enone accelerated Cope rearrangement to generate a bicylco[2.2.2]octanone ring system (330). Finally, the dienophiles prepared from the carbomagnesiation reaction were employed as …
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Total synthesis of ferrugine and synthetic studies towards ferrugine and stemofoline
… containing the 8-azabicyclo[3.2.1]octane ring system, are widespread in Nature. This thesis describes the total synthesis of the tropane alkaloid ferrugine, isolated from the arboreal species Darlingiana ferruginea and attempted synthesis of ferruginine, isolated from the arboreal species …
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A biosystematic study of Allium amplectens Torr
… and possibly their locations on the heterocyclic ring system, of the anthocyanins.
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Attempts to Synthesize 5-(P-Acetoxyphenyl)-3-Carbomethoxy- 4,6-Dicarboethoxy-Hexa-Hydroindanedione-l,7-Delta 3-9
… of the parent hydrocarbon, and have the ring system given in the structure below.
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Synthesis and properties of some 4H-1, 3, 4 benzothiadiazines /|nby Darko J. Vukov. -- 260 St. Catharines, Ont. : [s. n.],
… the synthesis of the 4H-l,3,4 benzothiadiazine ring system has been extended to 4H-l,3,4 benzothiadiazines with substituents in the 5 and 6-positions. Extension of synthesis also involves 4H-l,3,4 benzothiadiazines with mora than one substituent. Nuclear magnetic resonance spectra of 5 and 6 …
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Intramolecular [4+2] cycloadditions of conjugated ynones and related species ; Studies directed toward the total systhesis of glycinoeclepin A
… affords a product with a dihydroisobenzofuran ring system. For this reaction, we propose a mechanism in which a highly strained heterocyclic allene intermediate undergoes an unusual rearrangement leading to a 3-furfuryl carbene. A 1,2-C-H insertion then produces the polycyclic furan product. A …
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Geometrical Analogues of Purine Substrates (5-Methyladenine, Pyrolysis, Diazabiphenylene)
… As a model for the cyclobutadienopurine ring system, benzo{3,4}cyclobutadieno{1,2-d}imidazole was prepared by thermal extrusion of dinitrogen. As expected of biphenylene analogues with increased electron density in the four-membered ring, the benzocyclobutadienoimidazole underwent …
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The relationship between Centaur activity and ring formation
… have been observed around Centaurs, such as the ring system that was discovered around Chariklo during a stellar occultation (Braga-Ribas et al., 2014). A symmetric feature was observed around Chiron during an occultation (Ruprecht et al., 2015), and some interpret this feature to be possible …
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X-ray structural investigations of bromo-oxoditerpenoids and the nickel (II) chelate of a pyridoxal-amino acid intermediate
… attachment of two Schiff base units. The fused ring system of each unit reveals distortions from planarity.
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