Efficient Synthesis of 4-(2‘-Alkenyl)-2,5-dihydrofurans and 5,6-Dihydro-2H-pyrans via the Pd-Catalyzed Cyclizative Coupling Reaction of 2,3- or 3,4-Allenols with Allylic Halides
摘要:
In the absence of a base, palladium(II) catalysts, such as PdCl2, PdCl2(CH3CN)(2), Pd(OAc)(2), and [(pi-C3H5)PdCl](2), can catalyze the cyclizative coupling reaction of 2,3- or 3,4-allenols with allylic halides in DMA at room temperature to provide 2,5-dihydrofurans and 5,6-dihydro-2H-pyrans, respectively, in moderate to good yields. Under similar reaction conditions, nonsubstituted 2,3-allenol 1s affords bimolecular cyclizative coupling product 5s as the major product. The scope of the reaction and its mechanism have been studied briefly. On the basis of the experimental results, the transformation was believed to proceed via a divalent palladium-catalyzed pathway.
On the Gold-Catalyzed Intramolecular 7-<i>exo-trig</i>Hydroamination of Allenes
作者:Daniel Pflästerer、Praphasiri Dolbundalchok、Shahid Rafique、Matthias Rudolph、Frank Rominger、A. Stephen K. Hashmi
DOI:10.1002/adsc.201300154
日期:2013.5.3
allene side tethers were tested as substrates for a gold‐catalyzed7‐exo‐trig hydroamination reaction. The nucleophilicity of the aniline derivatives plays an important role for the outcome of the reaction. While electron‐deficient protecting groups at the nitrogen led to competing pathways like hydroarylation or an allene to diene isomerization, clean formation of the desired benzoxazepines was obtained
Intramolecularhydroarylation of allenes was achieved under very mild conditions using bismuth(III) triflate as the catalyst. Efficient functionalization of activated and nonactivated aromatic nuclei led to C–C bond formation through a formal Ar–H activation. A tandem bis-hydroarylation of the allene moiety was also developed giving access to various interesting polycyclic structures.