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Photochemical Conversion of Phenanthro[9,10-<i>d</i>]imidazoles into π-Expanded Heterocycles
Skonieczny, Kamil,Gryko, Daniel T. American Chemical Society 2015 Journal of organic chemistry Vol.80 No.11
<P>We discovered that phenanthro[9,10-<I>d</I>]imidazoles bearing a 2-halogenoaryl substituent at position 2 undergo swift photochemically driven direct arylation, leading to barely known phenanthro[9′,10′:4,5]imidazo[1,2-<I>f</I>]phenanthridines. The reaction is high-yielding, and it does not require any sensitizer or base. The discovered process is tolerant of a variety of substituents present both at positions 1 and 2; i.e., strongly electron-donating and electron-withdrawing substituents are tolerated as well as various heterocyclic units. Steric hindrance does not affect this process. The evidence gathered here indicates that S<SUB>RN</SUB>1 mechanism is operating in this case with the formation of radical anion as a critical step, followed by heterolytic cleavage of a carbon–halogen bond. Also TfO groups were shown to undergo cyclization, which allows the use of salicylaldehydes in the construction of heterocyclic systems. Efficiency of this photochemically driven direct arylation has been demonstrated by the synthesis of two systems possessing 13 and 17 conjugated rings, respectively. Phenanthro[9′,10′:4,5]imidazo[1,2-<I>f</I>]phenanthridines are blue-emitters, and they exhibit strong fluorescence in solution and in the solid state in direct contrast to their precursors.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/joceah/2015/joceah.2015.80.issue-11/acs.joc.5b00714/production/images/medium/jo-2015-00714j_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jo5b00714'>ACS Electronic Supporting Info</A></P>
Park, Ja-Young,Skonieczny, Kamil,Aratani, Naoki,Osuka, Atsuhiro,Gryko, Daniel T.,Lee, Chang-Hee The Royal Society of Chemistry 2012 Chemical communications Vol.48 No.65
<P>Calix[4]pyrroles bearing two proximally crossing straps on the same or the opposite sides have been synthesized for the first time. The doubly <I>cis</I>-strapped compound exhibited highly cooperative six-point hydrogen bonding interactions with the anion involving both pyrrolic N–Hs and Ar–Hs.</P> <P>Graphic Abstract</P><P>Calix[4]pyrroles bearing two proximally crossing straps on the same side or the opposite side have been synthesized and characterized. The <I>cis</I>-strapped compound encapsulates the fluoride anion strongly by six-point hydrogen bonding interaction while the <I>trans</I>-strapped compound shows very weak binding. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2cc33537a'> </P>