Metal-free Hydroalkoxylation-Formal [4+2] Cycloaddition Cascade for the Synthesis of Ketals
作者:Santosh J. Gharpure、Santosh K. Nanda、Padmaja、Yogesh G. Shelke
DOI:10.1002/chem.201701659
日期:2017.7.26
A transition metalfree, acid promoted cascade hydroalkoxylation–formal [4+2] cycloaddition of various alkynols with salicylaldehyde is demonstrated for the synthesis of tetrahydrofurano/pyrano‐chromenes and spiroketals. In general, alkynols underwent hydroalkoxylations in an endo‐dig manner when internal alkynes were used to furnish the heteroannular ketals, whereas terminal alkynes proceeded in an
Catalytic Generation and Selective Heterocoupling of Two Electron-Rich Alkenes
作者:Alicia Galván、Jonás Calleja、Francisco J. Fañanás、Félix Rodríguez
DOI:10.1002/anie.201209870
日期:2013.6.3
heterocyclic products were synthesized from simple alkynamine and alkynol derivatives in a double cycloisomerization/heterodimerization cascade reaction (see scheme). The reaction includes the heterocoupling reaction of two different electron‐richalkenes and leads to the formation of four new bonds and three stereocenters (two of them quaternary).
Intramolecular Endo-Dig Hydrosilylation Catalyzed by Ruthenium: Evidence for a New Mechanistic Pathway
作者:Barry M. Trost、Zachary T. Ball
DOI:10.1021/ja028766h
日期:2003.1.1
The ruthenium catalyst [Cp*Ru(MeCN)3]PF6 effects a novel intramolecular hydrosilylation of homo- and bis-homopropargylic alcohols, producing products of unique regioselectivity under very mild conditions with excellent selectivity. The reaction is compatible with a wide range of functional groups and tolerates substantial steric bulk. In addition to producing valuable synthetic intermediates thus far obtainable only in circuitous fashion, the results imply the necessity for a reexamination of the mechanism surrounding trans-hydrosilylation reactions, at least for ruthenium catalysts. At the very least, a simple cis addition/isomerization mechanism almost certainly cannot be active in this case. A silicon-ruthenium transposition could potentially provide a rationalization. However, the evidence for any products of syn addition with nonhydrido ruthenium catalysts is very scarce. Alternatively, a direct trans addition to orthogonal p-systems is also a possibility.
Stereo- and regioselective metal salt-catalyzed alkynylation of 1,2-epoxides
A simple, efficient, stereoselective, and highly regioselective method for the synthesis of beta-hydroxyacetylenes by the direct opening of 1,2-epoxides with lithium acetylides in anhydrous THF, in the presence of metal salts, is described. This new method appears to be competitive and alternative to the other methods previously reported.