Extensive halogen scrambling and buttressing effects encountered upon treatment of oligobromoarenes with bases
As a rule, tri-, tetra- and pentahaloarenes readily undergo ortho-lithiation when treated with amide-type bases. However, halogen migration occurs whenever the substrate contains three or more contiguous halogen atoms, provided that at least one of them is bromine or iodine. Dismutation and redn. processes often take place concomitantly. In this manner, a variety of organometallic intermediates may be formed, the driving force always being a decrease in basicity. When no such energy gain can be achieved, a sterically crowded substrate may just turn out to be inert, this was found to be the case with 1,5-dibromo-3-fluoro-2-(trimethylsilyl)benzene, 1,5-dibromo-3-fluoro-2,4-bis(trimethylsilyl)benzene, and 1,5-dibromo-3-fluoro-2,4-diiodobenzene. Buttressing effects are apparently strong enough to prevent expedient deprotonation of those substrates. [on SciFinder (R)]
2001
14
2771
2777
CAN 135:272713 25-3 Benzene, Its Derivatives, and Condensed Benzenoid Compounds Institut de Chimie organique de l'Universite,Lausanne,Switz. Journal 1434-193X written in English. 108-70-3 (1,3,5-Trichlorobenzene); 372-38-3 (1,3,5-Trifluorobenzene); 608-90-2 (Pentabromobenzene); 636-28-2 (1,2,4,5-Tetrabromobenzene); 1489-53-8 (1,2,3-Trifluorobenzene); 38227-87-1 (Lithium 2,2,6,6-tetramethylpiperidine); 93066-37-6 Role: RCT (Reactant), RACT (Reactant or reagent) (halogen scrambling and buttressing effects in treatment of oligobromoarenes with bases); 608-21-9P (1,2,3-Tribromobenzene); 634-89-9P (1,2,3,5-Tetrabromobenzene); 6324-50-1P (1,3,5-Trichloro-2-iodobenzene); 17299-95-5P; 41860-63-3P (1,3,5-Trifluoro-2-iodobenzene); 84322-55-4P (1,3,5-Trifluoro-2,4-diiodobenzene); 257621-23-1P (1,2,4,5-Tetrabromo-3-fluorobenzene); 363598-27-0P; 363598-34-9P; 459424-72-7P; 459425-36-6P Role: RCT (Reactant), SPN (Synthetic preparation), PREP (Preparation), RACT (Reactant or reagent) (halogen scrambling and buttressing effects in treatment of oligobromoarenes with bases); 50-43-1P (2,4,6-Trichlorobenzoic acid); 601-84-3P (2,6-Dibromobenzoic acid); 633-12-5P (2,4,6-Tribromobenzoic acid); 21739-99-1P (2,3,6-Tribromobenzoic acid); 22230-43-9P (2,3,4,5,6-Pentabromobenzoic acid); 36667-05-7P (2,3,4-Tribromobenzoic acid); 63165-48-0P (2,3,5,6-Tetrabromo-4-fluorobenzoic acid); 63165-49-1P (2,3,4,6-Tetrabromo-5-fluorobenzoic acid); 63165-50-4P (2,3,4,5-Tetrabromo-6-fluorobenzoic acid); 87976-24-7P (2,3,4,6-Tetrabromobenzoic acid); 87976-25-8P (2,3,5,6-Tetrabromobenzoic acid); 203916-59-0P (2,3,4-Trifluoro-5-iodobenzoic acid); 363598-23-6P; 363598-25-8P; 363598-28-1P; 363598-30-5P; 363598-32-7P; 363598-36-1P; 363598-38-3P; 459427-93-1P Role: SPN (Synthetic preparation), PREP (Preparation) (halogen scrambling and buttressing effects in treatment of oligobromoarenes with bases); 108-36-1 (1,3-Dibromobenzene); 626-39-1 (1,3,5-Tribromobenzene); 816-43-3 (Lithium diethylamide); 1435-51-4 (1,3-Dibromo-5-fluorobenzene); 2268-05-5 (1,3-Dichloro-2-fluorobenzene) Role: RCT (Reactant), RACT (Reactant or reagent) (halogen scrambling and buttressing effects of silyl group in reaction of oligobromoarenes with bases); 35997-04-7P; 183065-70-5P ((2,4-Dibromo-6-fluorophenyl)trimethylsilane); 363598-42-9P; 363598-44-1P; 363598-46-3P; 363598-48-5P; 363598-50-9P; 363598-52-1P; 363598-54-3P; 363598-55-4P Role: RCT (Reactant), SPN (Synthetic preparation), PREP (Preparation), RACT (Reactant or reagent) (halogen scrambling and buttressing effects of silyl group in reaction of oligobromoarenes with bases); 363598-40-7P Role: RCT (Reactant), SPN (Synthetic preparation), PREP (Preparation), RACT (Reactant or reagent) (inert; halogen scrambling and buttressing effects in treatment of oligobromoarenes with bases); 202982-76-1P (1,5-Dibromo-3-fluoro-2-iodobenzene) Role: RCT (Reactant), SPN (Synthetic preparation), PREP (Preparation), RACT (Reactant or reagent) (synthesis of diiodo deriv.)
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