Formation of Monosubstituted Arenes by Proton Abstraction

Beller et al. have reported a transition metal-free amination reaction of an aryl chloride in the presence of KOt-Bu by intermediate aryne formation (Equation 12.8) [10]. 

The reaction conditions are similar to the palladium-catalyzed Buchwald-Hartwig amination (see Chapter 3) with one distinct advantage when the base NaOt-Bu used in the Buchwald-Hartwig procedure is replaced with KOt-Bu, the reaction proceeds without the need for a palladium catalyst. Primary and secondary amines, as well as aromatic and aliphatic amines, undergo the amination smoothly however, only meto-substituted aniUnes can be obtained. 

Larock and coworkers have also reported the transition metal-free O-arylation of phenols and carboxyUc acids by arynes [11b, 13]. Phenols bearing either electron-donating or electron-withdrawing substituents react smoothly, leading to the corresponding diaryl ethers in excellent yields (Equation 12.9). 

The stericaUy hindered 2,4,6-trimethylphenol also worked weU, but ahphatic alcohols did not react weU with arynes under the reaction conditions. On the other hand, arene thiols reacted well with arynes, affording the desired S-arylated products in fairly good yields (Equation 12.10). 

In addition, the O-arylation of aromatic carboxylic adds with arynes proceeded smoothly under the reaction condihons, afTording the corresponding aryl esters in excellent yields (Equation 12.11). In contrast, aUphatic carboxylic acids afforded only low yields of esters. 

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