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101.
The ene reaction of sulfur dioxide with enoxysilanes or with allylsilanes generates silyl sulfinates that can be brominated (Br(2) or NBS) or chlorinated (NCS or Cl(2)) to produce the corresponding sulfonyl halides. They react with primary and secondary amines or alcohols to give the corresponding sulfonamides and sulfonic esters, respectively. The hetero-Diels-Alder addition of sulfur dioxide to 1-oxy- or 1,3-dioxy-1,3-dienes generates zwitterions that add to enoxysilanes or allylsilanes giving silyl sulfinates that can be converted in situ into polyfunctional sulfonamides or sulfonic esters. This realizes quick access to libraries of complicated sulfonamides and sulfonic esters applying one-pot, three- and four-component methods. 相似文献
102.
The α-D -allo-diol 9 possesses an intramolecular H-bond (HO? C(3) to O? C(1)) in solution and in the solid state (Fig. 2). In solution, it exists as a mixture of the tautomers 9a and 9b (Fig. 3), which possess a bifurcated H-bond, connecting HO? C(2) with both O? C(1) and O? C(3). In addition, 9a possesses the same intramolecular H-bond as in the solid state, while 9b is characterized by an intramolecular H-bond between HO? C(3) and O? C(4). In solution, the β-D -anomer 12 is also a mixture of tautomers, 12a and presumably a dimer. The H-bonding in 9 and 12 is evidenced by their IR and 1H-NMR spectra and by a comparison with those of 3–8, 10 , and 11 . The expected regioselectivity of glycosidation of 9 and 12 by the diazirine 1 or the trichloroacetimidate 2 is discussed on the basis of the relative degree of acidity/nucleophilicity of individual OH groups, as governed by H-bonding. Additional factors determining the regioselectivity of glycosidation by 1 are the direction of carbene approach/proton transfer by H-bonded OH groups, and the stereoelectronic control of both the proton transfer to the alkoxy-alkyl carbene (in the σ-plane) and the combination of the thereby formed ions (π-plane of the oxycarbenium ion). Glycosidation of 9 by the diazirine 1 or the trichloroacetimidate 2 proceeded in good yields (75–94%) and with high regioselectivity. Glycosidation of 9 and 12 by 1 or 2 gave mixtures of the disaccharides 14–17 and 18–21 , respectively (Scheme 2). As expected, glycosidation of 12 by 1 or by 2 gave a nearly 1:1 mixture of regioisomers and a slight preference for the β-D -anomers (Table 4). Glycosidation of the α-D -anomer 9 gave mostly the 1,3-linked disaccharides 16 and 17 (α-D β-D ) along with the 1,2-linked disaccharides 14 and 15 (α-D < β-D , 1,2-/1,3-linked glycosides ca. 1:4), except in THF and at low temperature, where the β-D -configurated 1,2-linked disaccharide 15 is predominantly formed. Similarly, glycosidation of 9 with 2 yielded mainly the 1,3-linked disaccharides (1,2-/1,3-linked products ca. 1:3 and α-D /β-D ca. 1:4). Yields and selectivity depend upon the solvent and the temperature. The regioselectivity and the unexpected stereoselectivity of the glycosidation of 9 by 1 evidences the combined effect of the above mentioned factors, which also explain the lack of regio-complementarity in the glycosidation of 9 by 1 and by 2 (Scheme 3). THF solvates the intermediate oxycarbenium ion, as evidenced by the strong influence of this solvent on the regio- and stereoselectivity, particularly at low temperatures, where kinetic control leads to a stereoelectronically preferred axial attack of THF on the oxycarbenium ion. 相似文献
103.
Transition-metal-catalyzed carbon-carbon bond-forming reactions are among the most powerful methods in organic synthesis and play a crucial role in modern materials science and medicinal chemistry. Recent developments in the area of ligands and additives permit the cross-coupling of a large variety of reactants, including inexpensive and readily available sulfonyl chlorides. Their desulfitative carbon-carbon cross-coupling reactions (Negishi, Stille, carbonylative Stille, Suzuki-Miyaura, and Sonogashira-Hagihara-type cross-couplings and Mizoroki-Heck-type arylations) are reviewed together with carbon-carbon cross-coupling reactions with other organosulfur compounds as electrophilic reagents. 相似文献
104.
A conceptually new total synthesis of oestrone, based on a novel cascade of radical cyclisations from the iodo aryl vinylcyclopropane 2, via 10, 15, 16 and 17, leading to the intermediate trans,anti,trans-oestradiol derivative 11 in one step, is described. Oxidation of 11, followed by demethylation of the resulting aryl methyl ether 18 then gives (±)-oestrone 1. 相似文献
105.
Vasu Govardhana Reddy P Suresh Reddy C Naga Raju C 《Chemical & pharmaceutical bulletin》2003,51(7):860-863
N-(substituted)-N'-(2,3-dihydro-5-benzoyl-2-oxido-1H-1,3,2-benzodiazaphosphol-2-yl) ureas were synthesized by reacting 3,4-diaminobenzophenone (4) with different chlorides of carbamidophosphoric acids (3) in the presence of triethylamine at 40-45 degrees C. Their 1H-, 13C- and 31P-NMR spectral data are discussed. The title compounds were screened for antifungal and antibacterial activity against the fungi Aspergillus niger and Fusarium solani and bacteria Escherichia coli and Staphylococcus aureus. These compounds showed higher antibacterial activity when compared with antifungal activity. 相似文献
106.
Indoles undergo smooth coupling with phenylacetylene in the presence of 10 mol % of gallium(III) chloride or gallium(III) bromide under mild conditions to afford the corresponding 1,1-bis(1H-3-indolyl)-1-phenylethanes in high yields and with high selectivity. 相似文献
107.
I. Sridhar Reddy P. Chandrasekhar Reddy B. Rangamannar 《Journal of Radioanalytical and Nuclear Chemistry》1991,153(5):333-338
An accurate and rapid radiochemical method has been developed for the determination of silver based on the substoichiometric extraction of its complex with potassium 3-phenylmethyldithiocarbazate into chloroform from pH 5.5 acetate buffer. Microgram amounts of silver could be determined with an average error of ±1.1% and the effect of diverse metal ions was critically examined. The method developed was applied to evaluate the silver content of photofilm washings. 相似文献
108.
109.
Tripathi RP Rastogi SK Kundu B Saxena JK Reddy VJ Srivastava S Chandra S Bhaduri AP 《Combinatorial chemistry & high throughput screening》2001,4(3):237-244
A library of 24 glycoconjugates related to glycosylated beta-amino acid derivative (I) was been prepared and screened against DNA topoisomerase-II of the filarial parasite S. cervi. Among these, compound 6 was found to be a potent inhibitor of DNA topoisomerase-II with 95% inhibition at 1.09 microM. Furthermore, compound 6 was at least three times more potent than the lead compound, glycosylated beta-amino acid derivative I. 相似文献
110.
Ch. Raji Reddy N. Kiranmai G. Dattatreya Sarma S. Chandrasekhar 《Tetrahedron letters》2007,48(2):215-218
The first use of hydroxylamine derivatives as the aminoxy equivalent of nucleophiles in palladium catalyzed addition to Baylis-Hillman acetate adducts is described. The reaction proceeds smoothly to give the substituted allyloxy amines in good yield and selectivity. 相似文献