Beyond Acid Strength in Zeolites: Soft Framework Counteranions for Stabilization of Carbocations on Zeolites and Its Implication in Organic Synthesis
作者:Jose R. Cabrero-Antonino、Antonio Leyva-Pérez、Avelino Corma
DOI:10.1002/anie.201500864
日期:2015.5.4
The generation of a carbocation with an acid depends not only on the acidstrength but also on the ability of the counteranion to stabilize the positive charge left behind. Here we report that despite their relatively weak acidity, zeolites are able to generate and stabilize medium‐size (molecular weight ≈300 Da) delocalized carbocations on their surface under mild reaction conditions, as it can be
Efficient synthesis of di- and trisubstituted 2-aryloxazoles via ytterbium(III) triflate catalyzed cyclization of tertiary propargylic alcohols with aryl amides
作者:Xiaoxiang Zhang、Wan Teng Teo、Philip Wai Hong Chan
DOI:10.1016/j.jorganchem.2010.09.059
日期:2011.1
based on Yb(OTf)3 catalyzed cyclization of trisubstituted propargylic alcohols with aryl amides is described. The reaction was accomplished in moderate to excellent product yields and with complete regioselective control. The mechanism is suggested to involve activation of the starting alcohol by the metal catalyst that results in its ionization. Subsequent cyclization of this newly generated carbocationic
A cesium carbonate promoted, transition metal and halogen‐free 5‐exo‐dig type cyclization reaction for the synthesis of oxazoles and imidazoles has been developed.
Three different substituted thiazoles have been successfully synthesized from readily available propargylic alcohols. Various secondary propargylic alcohols or tertiary propargylic alcohols participated well in the reaction, providing the desired products in good yields. This method provides a flexible and rapid route to substituted thiazoles.
SnCl<sub>2</sub>-Catalyzed Propargylic Substitution of Propargylic Alcohols with Carbon and Nitrogen Nucleophiles
作者:Yoshiro Masuyama、Miki Hayashi、Noriyuki Suzuki
DOI:10.1002/ejoc.201201673
日期:2013.5
higher catalytic activity than tin(II) bromide or iodide in the propargylic substitution of 1-phenyl-2-propyn-1-ol with anisole at 40 °C in CH3NO2. The solubility of tin(II) fluoride in CH3NO2 would have to be extremely low to cause no propargylic substitution. 1-Phenyl-substituted propargylic alcohols readily reacted with all these nucleophiles, whereas 1-(4-cyanophenyl)-2-propyn-1-ol and 1-(pentafluo
一种弱路易斯酸,氯化锡 (II),对水和空气不敏感,可用作仲炔醇与碳亲核试剂(如富电子芳烃、杂芳烃和 1,3-二羰基)炔丙基取代的催化剂化合物和氮亲核试剂,如磺酰胺、氨基甲酸酯和甲酰胺,在 40-80 °C 的 CH3NO2 中,在空气中,在 1-苯基-2-炔丙基取代中表现出比溴化锡或碘化锡(II)更高的催化活性propyn-1-ol 和苯甲醚在 40 °C 的 CH3NO2 中。氟化锡 (II) 在 CH3NO2 中的溶解度必须极低才能不引起炔丙基取代。1-苯基取代的炔丙醇很容易与所有这些亲核试剂反应,而 1-(4-氰基苯基)-2-丙炔-1-醇和 1-(五氟苯基)-2-丙炔-1-醇根本不与1,2, 3-三甲氧基苯甚至在 CH3NO2 中回流。1-烷基取代的仲炔醇,1,5-二苯基-1-戊炔-3-醇,经历了 SnCl2 催化的炔烃取代与富电子芳烃和酰胺,尽管即使在 80 °C 的 CH3NO2