ORGN 437 |
| With alkyllithium metalating agents, ortho-lithiation of p-BrA cannot be accomplished as halogen/metal exchange is the initial reaction path. With phenyllithium, ortho-lithiation can be achieved, but the generated by-product, benzene, is now considered hazardous. We advocate use of substituted aryllithium intermediates as surrogates for PhLi. Our ability to generate o-lithiodimethylaniline (o-LiDMA) in efficiencies >95% suggested that this reagent might be effective for lithiation of appropriate halogen-containing aryl substrates. This has now been demonstrated by our use of this protocol to afford o-TMS-p-BrA in good yield. This stable substance can be used to prepare a numerous combination of derivatives via the halogen (halogen/lithium exchange, Grignard formation, aryl coupling, etc.) as well as regiospecific introduction of other substituents by use of ipso-displacement of the TMS moiety. A series of o-substituted p-BrA's has been prepared in good yield via the readily prepared o-Li-p-BrA intermediate. These include those from treatment of the intermediate with cyclopentanone, iodine, Eschenmoser's salt, etc. Further amplification of this methodology to other suitable haloaryl sustrates will be discussed. |
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Heterocycles and Aromatics, Molecular Recognition and Self Assembly
8:00 PM-10:00 PM, Tuesday, April 8, 2008 Morial Convention Center -- Hall A, Poster
Sci-Mix
Division of Organic Chemistry |