868-26-8Relevant articles and documents
Lipophilic indole mediated chemoselective α-monobromination of 1,3-dicarbonyl compounds
Wong, Jonathan,Ke, Zhihai,Yeung, Ying-Yeung
, (2020/03/04)
A mild and efficient mono-selective bromination of 1,3-dicarbonyl compounds has been developed using lipophilic indole catalysts. Inexpensive and commercially available N-bromosuccinimide (NBS) was used as the brominating reagent. The selectivity was further enhanced when using stoichiometric amount of 3-bromoindole species. Mechanistic studies reveal that the indole catalyst has dual functions in the mono-bromination process.
Halogenation of carbonyl compounds by an ionic liquid, [AcMIm]X, and Ceric Ammonium Nitrate (CAN)
Ranu, Brindaban C.,Adak, Laksmikanta,Banerjee, Subhash
, p. 358 - 362 (2008/02/13)
An ionic liquid, acetylmethylimidazolium halide ([AcMIm]X), in combination with ceric ammonium nitrate promotes halogenations of a wide variety of ketones and 1,3-keto esters at the ?-position. The ionic liquid acts here as reagent as well as reaction medium, and thus the reaction does not require any organic solvent or conventional halogenating agent. The reaction is completely arrested when the radical quencher TEMPO is used. A plausible radical mechanism is also suggested. CSIRO 2007.
Synthesis and decarboxylation of Δ2-cephem-4,4-dicarboxylic acids
Wolfe,Ro,Kim,Shi
, p. 1238 - 1258 (2007/10/03)
Penicillin V was converted in 14 steps into Δ2-cephems having hydrogen at C-3, hydrogen or methyl at C-2, and two methoxycarbonyl, two benzyloxycarbonyl, or one methoxycarbonyl and one benzyloxycarbonyl substituent at C-4. Deprotection of these Δ2-cephem-4,4-dicarboxylic acid esters by alkaline hydrolysis (in the case of methyl esters) or hydrogenolysis (in the case of benzyl esters) led in all cases to rapid decarboxylation of the Δ2-cephem-4,4-dicarboxylic acid or Δ2-cephem-4,4-dicarboxylic acid monoester. With hydrogen at C-2, hydrolysis of the dimethyl ester with 1 equiv of base produced a Δ2-cephem. With 2 equiv of base, and with all compounds having methyl at C-2, hydrolysis or hydrogenolysis afforded 4α-substituted-Δ2-cephems. In contrast, simpler benzyl or methyl acetamidomalonates could be deprotected without difficulty to afford stable malonic acids. Reasons for the differences in ease of decarboxylation were examined using semiempirical (AM1) and ab initio (3-21G) molecular orbital calculations. The decarboxylation barriers of unionized cephem or acetamido malonic acids were found to be high (35-40 kcal mol-1). Although the monoanion of acetamidomalonic acid retained a high barrier, the epimeric monoanions of a Δ2-cephem malonic acid decarboxylated with barriers of only 2 kcal mol-1.