Mechanistic Studies and Improvement of Coinage Metal-Catalyzed Transformation of Alkynyloxiranes to Furans: An Alcohol Addition−Cyclization−Elimination Cascade
摘要:
In the presence of alcohol Ag or Au salts or complexes catalyze the conversion of alkynyloxiranes to substituted furans. Both-catalysts are effective, and a large furan diversity can be obtained in high yield with one or the other catalyst. Mechanistic studies revealed that a cascade pathway and not the sometimes reported direct intra molecular nucleophilic addition of oxirane oxygen atom to intermediate acetylene-metal pi-complex occurs. Under the defined conditions, the intermediate formation of epoxide opening products has been identified. Depending on the catalyst, one or both of the latter cyclized to dihydrofurans, and further elimination of the alcohol led to the corresponding furans. These results highlight the duality between oxophilicity and alkynophilicity of Ag or Au salts.
Bulky Trialkylsilyl Acetylenes in the Cadiot−Chodkiewicz Cross-Coupling Reaction
作者:Joseph P. Marino、Hanh Nho Nguyen
DOI:10.1021/jo025745x
日期:2002.9.1
tert-butyldimethylsilyl (TBS), and triisopropylsilyl (TIPS) acetylenes underwent the Cadiot-Chodkiewicz cross-coupling reaction with different bromoalkynes to form a variety of synthetically useful unsymmetrical diynes in good yields. The diyne alcohol 10 was transformed regio- and stereoselectively into enynes by hydrotelluration, carbometalation, and reduction reactions.
The intermolecular deacylative coupling of unstrained ynones via C-C bond activation was accomplished by a CuCl-bpy system undermild reaction conditions. This protocol features facile cleavage of the C-C bond at room temperature, broad substrate scope, and efficient construction of important symmetric and unsymmetrical 1,3-diyne adducts through homo or cross coupling of ynones, respectively. The preliminary
Palladium-catalyzed oxidative homocoupling of terminalacetylenes, in air, occurred in the presence of 1-(2-pyridylethynyl)-2-(2-thienylethynyl)benzene as ligand, affording the corresponding conjugated diynes.
The Unprecedented Cobalt-Catalysed
Oxidative Glaser Coupling under Reductive Conditions
作者:Gerhard Hilt、Christoph Hengst、Marion Arndt
DOI:10.1055/s-0028-1083316
日期:——
The cobalt-catalysed Glaser-type coupling of terminal alkynes was achieved utilising nitrobenzene as a stoichiometric oxidising agent under reductive conditions. The proposed electron transfer from zinc powder to a nitrobenzene coordinated to the cobalt centre initiates the coupling of the coordinated alkynes. Other aryl-, alkenyl-, alkyl-, and silylacetylenes besides phenylacetylene could also be coupled to generate the 1,3-diynes in moderate to very good yields.
We developed a technique mediated by visible light for the aerobic homocoupling of terminal alkynes to synthesize 1,3-conjugated diynes using a copper(I) chloride catalyst at room temperature. Compared with previously reported thermal processes, this photochemical method is simple, uses only mild reaction conditions, produces high yields and works well for substrates with electron-withdrawing groups