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71.
Treatment of methyl 2,3-O-isopropylidene-β-
-ribofuranoside with DAST gave a goodyield of 2,3-O-isopropylidene-5-O-methyl-β-
-ribofuranosyl fluoride in which the methoxygroup had migrated from C-1 → C-5 and been replaced with retention of configurationby fluorine. The corresponding aldehyde when treated under similar conditions underwenta similar migration to give 5-deoxy-5-fluoro-2,3-O-isopropylidene-5-O-methyl-β-
-ribofuranosylfluoride. A similar migration occurred with methyl 2′,3′-di-O-acetyl-β-
-ribofuranosideand with acetyl 2,3-O-isopropylidene -
-ribofuranose but not with 1,2,3-tri-O-acetyl-
-ribofuranose. Thus the migration depends upon the migratory aptitude of thesubstituent at C-1 and the conformation of the furanose ring. Two ribofuranosyl fluorideswere used as starting materials from which to make nucleosides by the method of Noyoriand Hayoshi. 相似文献
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Riggs JC Ramirez A Cremeens ME Bashore CG Candler J Wirtz MC Coe JW Collum DB 《Journal of the American Chemical Society》2008,130(11):3406-3412
The key elimination step for the formation of 3-substituted and 3,6-disubstituted benzynes from 2-haloaryllithiums displays a pronounced solvent-dependent regioselectivity. All 2-haloaryllithiums with electron withdrawing groups in the 6 position are shown by 6Li and 13C NMR spectroscopic studies to be monomers in THF. DFT computational studies implicate trisolvates. Rate studies reveal that LiF eliminates via monomer-based pathways requiring THF dissociation whereas LiCl eliminates via nondissociative pathways. Elimination to form 3-chloro- and 3-fluorobenzyne from 2-chloro-6-fluorophenyllithium displays a pronounced solvent-dependent regioselectivity that is traced to competing solvent-dissociative and nondissociative dissociative pathways for the elimination of LiCl and LiF, respectively. 相似文献
74.
Coe BJ Harris JA Brunschwig BS Garín J Orduna J 《Journal of the American Chemical Society》2005,127(10):3284-3285
We have used several techniques, including Stark spectroscopy and MO calculations, to investigate the optical and electronic properties of two new dipolar chromophoric cations containing diquat-based electron acceptor groups. Both the Stark data and the calculated parameters show that the strong electron-accepting properties of a diquat unit lead to static first hyperpolarizabilities beta0 which are considerably larger than those of a related stilbazolium chromophore. In addition, one compound has a strongly 2D quadratic NLO response, providing a very rare example of a charged molecule displaying such behavior. 相似文献
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H Machner M Betigeri J Bojowald A Budzanowski A Chatterjee J Ernst L Freindl D Frekers W Garske K Grewer A Hamacher J Ilieva L Jarczyk K Kilian S Kliczewski W Klimala D Kolev T Kutsarova J Lieb H Machner A Magiera H Nann L Pentchev HS Plendl D Protić B Razen P Von Rossen BJ Roy R Siudak J Smyrski RV Srikantiah A Strzałkowski R Tsenov K Zwoll 《Pramana》2001,57(2-3):399-416
Total and differential cross sections for the reactions p + d → 3He + m
0 with m=π, η and p + d → 3H+π+ were measured with the GEM detector at COSY for beam momenta between threshold and the maximum of the corresponding baryon
resonance. For both reactions a strong forward-backward asymmetry was found. The data were compared with model calculations.
The aspect of isospin symmetry breaking is studied.
Representing the GEM Collaboration 相似文献
80.