Some Reactions of o-Halobromobenzenes with n-Butyllithium

Synthesis of fluorinated analogues of the neurosteroid GABAA receptor antagonist, 17-PA

“…The increased acidity of the hydrogen atom ortho to the fluorine atoms clearly results in a competing lithium-hydrogen exchange, leading to a mixture of 1,3-difluorophenyl-5-lithium 14 and 1,3-difluorophenyl-2-lithium 15 giving rise to product mixture of 12 and 13 after reaction with androsterone (Scheme 3). Generally, fluorinated phenyllithiums are stable only at low temperature and in the case of ortho-fluorophenyllithiums, LiF elimination occurs above À50 8C to generate benzynes [13][14][15][16]. Thus this proved to be an inefficient reaction.…”

“…(3a,5a,17b)-(17-p-Toluene)androstane-3,17-diol(16) n-BuLi (2 cm 3 , 2.5 M in hexane, 5.0 mmol) was added at RT under N 2 to a solution of p-bromotoluene (860 mg, 5.0 mmol) in dry diethyl ether (5 cm 3 ). The mixture was stirred for 2 h at RT and added dropwise via cannula to a solution of androsterone (262 mg, 0.9 mmol) in dry THF (10 cm 3 ).…”

Selective Halogen-Lithium Exchange of 1,2-Dihaloarenes for Successive [2+4] Cycloadditions of Arynes and Isobenzofurans

“…Moreover, the corresponding reaction of iodide 8c having a fluorine atom at 2-position as a leaving group gave moderate yield of 6a (entries 5-6). These results indicate that halogen-lithium exchange selectively occurred at the more electropositive iodine atom in iodo-halides 8a-8c (Type 1 in Scheme 3), smoothly generating (2-halo)phenyllithiums, respectively, whereas the dibromoisobenzofuran 1 and the dibromocycloadduct 6a almost untouched under these conditions [33][34][35][36]. As for the moderate yield of the cycloadduct 6a in the reaction of the dihalides 8b and 8c, the lower leaving ability of halogen (Cl and F) in comparison with bromine in aryllithium species would affect the elimination of lithium halide and subsequent generation of benzyne B [37].…”

Is Carbon Dioxide Able to Activate Halogen/Lithium Exchange?

“…The aqueous phase was extracted with Et 2 O (2 × 10 mL) and solvents were evaporated to give the crude product, which was washed with water, hexane (2 × 5 mL) and dried in air, yield 1.09 g (78 %); m.p. 123–125 °C (ref 66. m.p.…”