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DOI: 10.1055/sos-SD-002-00214

Kündig, E. P.; Pache, S. H.Science of Synthesis, (20032168.

The electrophilic tricarbonylchromium group activates the arene ring toward nucleophilic attack. Chlorobenzene complexes readily undergo SNAr substitution of chloride by hydroxide, alkoxide (e.g., 34 35, 39 40),[‌110‌] phenoxide (e.g., 38 39),[‌111‌] and thiolate nucleophiles as well as by sodium hydride/trifluoroacetamide (e.g., 36 37) (Scheme 8).[‌112‌] The reaction is particularly efficient under phase-transfer conditions, in benzene in the presence of crown ethers, or in dimethyl sulfoxide. In contrast, more reactive carb­anions preferentially add ortho to the chlorobenzene complex 6 (M=Cr; R1=Cl) and ipso substitution is feasible only for nucleophiles that add reversibly. The fluoro complex 6 (M=Cr; R1=F) is even more reactive: in dimethyl sulfoxide, fluoride is substituted by a wide range of nucleophiles that include alkoxides, carboxylates, amines, and a variety of carbanions ranging from acetylides to ketone enolates.[‌113‌,‌114‌] An example of an intramolecular reaction is shown by the transformation 41 42.[‌115‌]

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