Arynes deprotonation

Arynes are formed when haloarenes are treated with a strong base. Deprotonation at the ortho position of the halogen atom is favored because of polarity alternation, and the facility ofbenzyhe formation from halobenzene (PhF > PhCl > PhBr p Phi) also corresponds with the relative strength of the donor. 

The preferred site of deprotonation of di- or polysubstituted arenes is not easy to predict. In 1,3-disubstituted benzenes in which both substituents facilitate ortho-metalation, deprotonation will usually occur between these two groups [181, 365, 408, 416-419] (Scheme 5.45). Dialkylamino groups, however, can sometimes deactivate ortho positions (fourth reaction, Scheme 5.45), but this does not always happen [181, 420], 3-Chloroanisole [411] and 3-fluoroanisole [421] are deprotonated by organolithium compounds between the two functional groups, but the lithiated arenes dimerize readily at -78 °C, presumably via intermediate aryne formation (last example, Scheme 5.45). 

More recently, the coupling of a nitrile with two molar equivalents of an aryne under mild conditions, has been reported by Yoshida et al. (Scheme 12.12) [29]. The fluoride anion used in this case acted not only as an aryne generator but also as a base to deprotonate the nitrile. This reaction proceeds in a manner similar to... 

Deprotonation. The o-metalation of aromatic halides is a weU-established route to arynes. In cases where the starting material contains two different halogens in 1,3-positions, the deprotonation reaction occurs at 2-position and then the elimination may lead to two different aryne derivatives depending on the halide anion that suffers the elimination reaction. In this context, the solvent of the reaction plays a crucial role. Thus, for example, in the case of 3-fluoro-l-chlorobenzene, the... 

The current experiment involves the preparation of the sterically hindered amine A -ferf-butyl-3,5-dimethylaniline. Other preparations of this amine involve addition of methyllithium to lV-3,5-dimethylphenylacetone imine and the reaction of l-bromo-2,4-dimethylbenzene with terf-butylamine either via aryne formation or by palladium-catalyzed alkylation. The current method, the reaction of tert-butylamine with the 2,4,6-trimethylpyrylium cation, involves inexpensive starting materials and proceeds in high yield. The molybdenum(III) complex of the deprotonated form of this amine, Mo[N(f-Bu)(3,5-C6H3Me2)]3, splits the N=N triple bond in N2 to afford molybdenum(VI) nitrido products. This latter reaction is the key step in the recently discovered catalytic process to convert N2 to ammonia under ambient conditions. 

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