Reagent-modulated optional site selectivities: the metalation of o-, m- and p-halobenzotrifluorides

Chloro(trifluoromethyl)benzenes and bromo(trifluoromethyl)benzenes underwent deprotonation at a postion adjacent to the single halogen substituent when treated with alkyllithiums (at -75 DegC) and, resp., lithium 2,2,6,6-tetramethylpiperidide (at -100 DegC) in THF. Positional ambiguities, if existing, were be exploited to establish optional site selectivities. Thus, the reaction of butyllithium with 1-chloro-3-(trifluoromethyl)benzene led to hydrogen/metal interconversion at the 2-position whereas the reaction of sec-butyllithium led exclusively to a reaction at the 6-position. The latter mode of regioselectivity was also exhibited by 1-bromo-3-(trifluoromethyl)benzene in the presence of lithium 2,2,6,6-tetrmethylpiperidide, and only 2-bromo-4-(trifluoromethyl)phenyllithium was produced. 2-Bromo-6-(trifluoromethyl)phenyllithium was directly inaccessible, but was formed when 2-bromo-3-(trifluoromethyl)phenyllithium, (generated at -100 DegC) was allowed to isomerize at -75 DegC. [on SciFinder (R)]


Published in:
Tetrahedron Letters, 37, 16, 2767-70
Year:
1996
Keywords:
Note:
CAN 125:10305
25-17
Benzene, Its Derivatives, and Condensed Benzenoid Compounds
Inst. Chimie Organique de l'Universite,Batiment de Chimie (BCh),Lausanne-Dorigny,Switz.
Journal
0040-4039
written in English.
88-16-4 (2-Chlorobenzotrifluoride); 98-15-7 (3-Chlorobenzotrifluoride); 98-56-6 (4-Chlorobenzotrifluoride); 392-83-6 (2-Bromobenzotrifluoride); 401-78-5 (3-Bromobenzotrifluoride); 402-43-7 (4-Bromobenzotrifluoride) Role: RCT (Reactant), RACT (Reactant or reagent) (reagent-directed regioselective metalation of halo(trifluoromethyl)benzenes); 328-89-2P; 657-06-7P; 1483-56-3P; 2376-00-3P; 23228-45-7P; 39226-97-6P; 177420-63-2P; 177420-64-3P Role: SPN (Synthetic preparation), PREP (Preparation) (reagent-directed regioselective metalation of halo(trifluoromethyl)benzenes); 109-72-8 (Butyllithium); 598-30-1 (sec-Butyllithium); 38227-87-1 (Lithium 2,2,6,6-tetramethylpiperidide) Role: RCT (Reactant), RACT (Reactant or reagent) (reagent; reagent-directed regioselective metalation of halo(trifluoromethyl)benzenes)
Laboratories:




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