Butyllithium Fries rearrangement

Fries rearrangement.1 Rearrangement of phenyl esters with Lewis acids results in a mixture of ortho- and para-phenolic ketones. In contrast, reaction of an o-bromophenyl ester with sec-butyllithium results in exclusive formation of the orf/jo-phenolic ketone by an intramolecular acyl rearrangement.2... 

Ortho-specific metal-promoted Fries rearrangement can be achieved, starting from orffeo-bromophenyl esters and sec-butyllithium. The reaction is performed at -95°C with 4 1 1 tetrahydrofuran diethyl ether hexane ratio followed by stirring for 30 min, followed by an additional 30 min at 78°C. The orfto-hydroxyaryl ketones are the sole isomers obtained, and the regioisomeric para-hydroxyaryl ketones are not obtained (Table 5.11). 

Table 5.11 sec-Butyllithium-promoted Fries rearrangement of ort/zo-bromophenyl esters... 

Anionic ortho-Fries rearrangement is performed by freafment of variously subsfifufed aryl carbamates with sec-butyllithium at -78°C in tetramethylethylenediamine-tetrahydrofuran solution for 8-12 h. i The reaction involves the selective ortho-metalation of fhe aryl groups. The meta-cooperafive mefalafion effect is responsible for fhe producfion of some extremely hindered aromatic compounds (Table 5.13). 

Preparation from 2-iodophenyl p-anisate on treatment with n-butyllithium in a mixture of ethyl ether, hexane and tetrahydrofuran at -70° for 2 h, followed by treatment with saturated aqueous ammonium chloride (<18%) [58]. Preparation by Fries rearrangement of phenyl p-anisate in the presence of aluminium chloride [897]. 

Also obtained by reaction of sec-butyllithium on 2-bromo-4,6-di-tert-butylphe-nyl acetate in ethyl ether at -95° and -78°, followed by hydrolysis of mixture with saturated ammonium chloride (metal-promoted Fries rearrangement) (43-52%) [3648]. 

Also obtained by reaction of 2-bromophenyl propionate in a ethyl ether/hexane/ THF mixture at low temperature (-78 to -95°) with sec-butyllithium to give, after hydrolysis, the titled ketone (metal-promoted Fries rearrangement) (17%) [6590]. 

Also obtained by reaction of sec-butyllithium (1.1 equiv) with 2-bromo-4,6-dimethylphenyl propionate in tetrahydrofuran/ethyl ether/hexane at -95° for 30 min and -78° for 30 min, then hydrolysis with saturated ammonium chloride (31%) (Metal-promoted Fries rearrangement) [6590]. 

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