Beilstein J. Org. Chem.2008,4, No. 13, doi:10.3762/bjoc.4.13
electron withdrawing behavior to the alkoxy group but also acts to deactivate the aromatic ring system [53].
Electrophilic AromaticSubstitution
Trifluoromethoxybenzene, for example, undergoes nitration considerably (up to 5 times) more slowly than benzene. The electrophilic substitution occurs selectively
Beilstein J. Org. Chem.2007,3, No. 22, doi:10.1186/1860-5397-3-22
them from participating as electrophiles in aromaticsubstitution reactions.
Conclusion
The useful imidazolium salts IPr·HCl (1), IMes·HCl (2) and IXy·HCl (3) have previously been synthesized by a range of methods giving the products in variable purity and yields. We now present a protocol for the
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Graphical Abstract
Figure 1:
The carbenes IPr, IMes, IXy and their imidazolium salt precursors