Ring-Opening of 4-Isoxazolines: Competitive Formation of Enamino Derivatives and a,b-Enones
摘要:
Ring-opening of 3-substituted 4-isoxazolines, proceeding through the intermediate isoxazolinium salts, follows two competing reaction pathways leading to alpha,beta-enones and enamines respectively. The rearrangement courses can be controlled as a function of substitution pattern and experimental conditions.
amount of InCl3 and aceticanhydride remarkably promotes the Knoevenagel condensation of a variety of aldehydes and activated methylene compounds. This catalytic system accommodates aromatic aldehydes containing a variety of electron-donating and -withdrawing groups, heteroaromatic aldehydes, conjugate aldehydes, and aliphatic aldehydes. Central to successfully driving the condensation series is the formation
CBr<sub>4</sub> as a Halogen Bond Donor Catalyst for the Selective Activation of Benzaldehydes to Synthesize α,β-Unsaturated Ketones
作者:Imran Kazi、Somraj Guha、Govindasamy Sekar
DOI:10.1021/acs.orglett.7b00348
日期:2017.3.3
CBr4 has been employed as a halogen bond donor catalyst for the selective activation of aldehyde, to achieve an efficient solvent- and metal-free C═C bond forming reaction in the presence of strong acid sensitive groups such as methoxy, cyanide, ester, and ketal for the synthesis of α,β-unsaturated ketones. This unique capability of CBr4 to act as a halogen bond donor has been explored and established
Asymmetric Total Synthesis of (−)-Plicatic Acid via a Highly Enantioselective and Diastereoselective Nucleophilic Epoxidation of Acyclic Trisubstitued Olefins
作者:Bing-Feng Sun、Ran Hong、Yan-Biao Kang、Li Deng
DOI:10.1021/ja9039407
日期:2009.8.5
The first total synthesis of (-)-plicatic acid has been achieved by a concise and enantioselective route. In this synthesis, a conceptually new strategy featuring an asymmetric epoxidation-intramolecular epoxy-ring-opening Friedel-Crafts reaction sequence was developed for the stereoselective construction of the 2,7'-cyclolignane skeleton bearing contiguous quaternary-quaternary-tertiary stereocenters
Catalyst-free chemoselective reduction of the carbon–carbon double bond in conjugated alkenes with Hantzsch esters in water
作者:Qi He、Zhihong Xu、Dehong Jiang、Wensi Ai、Ronghua Shi、Shan Qian、Zhouyu Wang
DOI:10.1039/c3ra48072k
日期:——
A simple, efficient and green protocol for chemoselective reduction of carbon–carbon doublebond in conjugated alkenes with Hantzsch esters is described. Without any additional catalysts, a series of conjugated alkenes with strong electron-withdrawing groups were reduced in water with excellent yield. Functional groups such as nitrile, ester, nitro, fluoro, chloro, bromo, furanyl and benzyl are all
Rearrangement of Propargylic Esters: Metal-Based Stereospecific Synthesis of (<i>E</i>)- and (Z)-Knoevenagel Derivatives
作者:José Barluenga、Lorena Riesgo、Rubén Vicente、Luis A. López、Miguel Tomás
DOI:10.1021/ja072864r
日期:2007.6.1
catalysts perform the isomerization with complementary Z/E selectivity. Moreover, alkynyl-conjugated Knoevenagel products are produced from (bisalkynyl)methyl acetates. In such a case, the reaction is chemoselective as the 1,3-acetyl migration takes place through the alkoxyalkyne group in preference over the phenylalkyne group. The resulting (E)-alkynylenone unit suffers metal-catalyzed cyclization