Addition fluoroarenes

Suzuki and co-workers achieve aromatic substitution of fluoroarenes with a variety of aldehydes in good yields [91, 92], Imidazolilydene carbene formed from 143 catalyzes the reaction between 4-methoxybenzaldehyde 22a and 4-fluoroni-trobezene 141 to provide ketone 142 in 77% yield (Scheme 20). Replacement of the nitro group with cyano or benzoyl results in low yields of the corresponding ketones. The authors propose formation of the acyl anion equivalent and subsequent addition to the aromatic ring by a Stetter-like process forming XXVIII, followed by loss of fluoride anion to form XXIX. 

The addition of two nucleophiles to a coordinated //6-arene is a synthetically important goal. A one-pot synthesis of 1,3-disubstituted cyclohexadienes involving an initial ipso addition to fluoroarene complexes is possible. Indeed, p-fluorotoluenetricarbonylchromium complex 22c reacts with isobutyronitrile carbanion (2 equiv.) in THF to give, after 5 days at —30 °C and acidic treatment under CO atmosphere, the cyclohexadiene 66 in 47 % yield (Scheme 31) [53] the yield can reach 75 % after several weeks Carbon monoxide was used in order to decoordinate the // -cyclohexadiene intermediate and to recover Cr(CO)6 needed for the preparation of the starting material [54]. 

A reaction similar to the overall copper-halogen exchange observed on addition of perhaloarenes to lithium dimethylcuprate is also given by pentafluorobenzene, pentachlorobenzene, 2,3,5,6-tetrachloropyridine (146), and tetrafluorobenzenes (144). A small excess of methyllithium was again required, otherwise the reactions were very slow. Formation of methylcopper during the addition was not observed with the poly-fluoroarenes, but a mechanism was proposed similar to that for the perhaloarenes (146). Equation (22) represents the overall reaction for pentafluorobenzene. In most cases, methane was evolved nearly quantitatively. 

Lithiation. A molecule featuring both a fluoroarene and a bromoarene subunit gives rise to aryne and lithioarene moieties on the treatment with t-BuLi. If such reactive components are spatially interactable, intramolecular addition can occur. ... 

Dediazotization. Aryldiazonium ions react at 80° with this sytem to give fluoroarenes. If sodium chloride, bromide, or iodide is added haloarenes are formed in good yield with less than 10% of fluoroarenes. However, the reaction gives unexpected and novel isomer distributions of haloarenes. That is, the halide ion attacks ring positions in addition to the one (Ci) from which N2 is lost. The results are rationalized on the basis of the ambident nature of aryldia-... 

Oxidative addition of C-F bonds to low-valent metal complexes constitute one of the routes in activation of fluoroalkanes and fluoroarenes [71, 72], The chemical activation of carbon-fluorine bonds has attracted much attention since functionalization of C-F compounds gives various fluoroorganic derivatives, which have many technological applications. Typical examples of oxidative addition of C-F bonds [73] are shown in Scheme IV.36. 

The 6-substituted phenanthridines 98 have been prepared by a one-pot coupling of fluoroarenes with nitriles (Scheme 12.29) [57]. Ortho-lithiation of fluorobenzene with t-BuLi led to o-fluorophenyllithium (96), and benzyne was subsequently generated from 96 by the loss of liF. A nucleophiUc addition of 96 to benzyne led to the formation of biaryl lithium species 97, while product 98 was generated after nucleophihc addition of 97 to a nitrile and subsequent intramolecular SnAt reaction. 

Bajo S, Esteruelas MA, Lop AM, Onate E. Reactions of an osmium bis(dihydrogen) complex under ethylene phosphine addition to a C—C double bond and C—H bond activation of fluoroarenes. Organometallics. 2011 30 5710-5715. 

Fluoroarenes may readily enter nucleophilic addition/nucleofugal elimination sequences. Hexafluorobenzene reacts with organolithiums with amazing ease. " ... 

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