Polyhalo-organometallic and -organometalloidal compounds

Metalation and Derivatization of All Six Dichlorobenzotrifluorides:Site Selectivities

“…Although this is a rare process, analogies featuring several polychloroarenes (e.g. 1,2,3-trichlorobenzene, [6,26] 1,2,3,4-tetrachlorobenzene, [26] and hexachlorobenzene [27] ) have been documented. 2,4-Dichloro-3-(trifluoromethyl)benzoic acid (25) is the expected "ortho-metalation" product derived from an intermediate bearing the metal atom at a chlorineadjacent position whereas the isomeric 3,5-dichloro-4-(trifluoromethyl)benzoic acid (26; identified by NMR spectroscopy as a byproduct after reductive dechlorination [11,[21][22][23] of the crude reaction mixture) is obviously the result of a "meta-directed metalation" reaction.…”

Aromatic and Alkaromatic Chlorocarbons

“…Pentachlorophenyllithium (XVIII) has been prepared by Rausch and co-workers [208], and other authors [58,203,[209][210][211][212][213][214][215][216] , also by metal-halogen exchange with n-butyllithium at low temperatures (--70°C), generally in THFl…”

“…An excess of alkyllithium leads to tetrachloro.p-phenylenedilithium (XIX) [216]. These metallations are of synthetic value, particularly in the formation of perchlorobenzyne.…”

Polychloroheteroaromatic Compounds

“…In the case of t-butyl-lithium, the lithium compound is formed exclusively in tetrahydrofuran but, with methyl-or n-butyl-lithium in the same solvent, considerable ringfragmentation also occurs [146]. Ring-fragmentation also occurs in the case of phenyl-lithium but to a lesser extent.…”

“…With one equivalent of n-butyl-lithium in ether [141,[143][144][145] or tetrahydrofuran [1461 at _70 0 , or methyl-, t-butyl-, or phenyllithium in tetrahydrofuran at _70 0 (146], tetrachlorothiophen gives trichloro-2-thienyl-lithium. In the case of t-butyl-lithium, the lithium compound is formed exclusively in tetrahydrofuran but, with methyl-or n-butyl-lithium in the same solvent, considerable ringfragmentation also occurs [146].…”