Gold- or Palladium-Catalyzed Allene Carbocyclization/Functionalization: Simple and Efficient Synthesis of Carbazoles
作者:Benito Alcaide、Pedro Almendros、José M. Alonso、M. Teresa Quirós、Paweł Gadziński
DOI:10.1002/adsc.201100209
日期:2011.8
Gold- and palladium-catalyzed cyclization of easily accessible indole-tethered allenols allows the efficient synthesis of carbazole derivatives under mild conditions.
2-(Pyridinium-1-yl)-1,1-bis(triflyl)ethanides have been used as 1,2-dipole precursors in a metal-free direct [2+2] cycloaddition reaction of alkynes. Remarkably, this mild and facile uncatalyzed protocol requires neither irradiation nor heating.
HCl or AcCl, at the central carbon of the mu-eta(3)-allenyl/propargyl ligand to give the mu-eta(3)-vinylcarbenedipalladium complexes. Intramolecular reaction proceeded smoothly to give cyclization products quantitatively. Addition of a catalytic amount of a palladium(0) complex dramatically accelerated the carbon-carbonbondformation. The MO calculations on the mu-eta(3)-allenyl/propargyl complexes indicated
in simultaneous control of multiple chiralities. In this article, we have succeeded in the perfectly diastereo- and enantiocontrolled catalytic synthesis of a cycloparaphenylene with four helical and two planar chiralities showing good chiroptical responses as chiral organic molecules. The perfectly stereocontrolled multiply helical structure was confirmed by a single-crystal X-ray diffraction analysis