Reduction of Aryl Halides by Lithium Dialkylamides

Abstract

The formation of anisóle from the reactions of various lithium dialkylamides with o-bromoanisole was investigated. It was established that the dialkylamide ion is concomitantly oxidized as the aryl halide is reduced. Thus lithium benzylmethylamide when treated with o-bromoanisole was oxidized to 2,5-diphenylpyrazine; lithium dibenzylamide to 2,3,5,6tetraphenylpyrazine; and lithium 6¿s-(p-methoxybenzyl)amide to 2,3,5,6-tetra-(p-methoxyphenyl)pyrazine.That the initial oxidation product might be an imine was demonstrated when lithium benzylmethylamide reacted with Nbenzilidinemethylamine to give 2,5-diphenylpyrazine. Also lithium dibenzylamide when treated with N-benzilidinebenzylamine gave 2,3,5,6-tetraphenylpyrazine.A possible reaction mechanism which is consistent with these findings is presented.

The Chemistry of Imines.

“…NC(CH2)4CN + NaNR2 -Mosher (186) has shown that Benkeser's (19) hypothesis that 2-bromoanisole reacts with the lithium amide of a secondary amine containing an a-hydrogen to give an imine is correct. He finds that N-2,2dimethylpropylidene-2',2'-dimethylpropylamine, a very stable imine, is formed when lithium [diisobutylamide reacts with 2-bromoanisole.…”

The Benzyne and Related Intermediates.

“…The degree of rearrangement in aminations of substituted halo benzenes with alkali amides is influenced by the position of the substituent relative to the halogen. Two factors must be considered: (1) factors governing the formation of particular benzyne isomers; (8) the effect of substituents on the direction of addition to the aryne.…”

π‐Strain‐Induced Electrophilicity in Small Cycloalkynes: A DFT Analysis of the Polar Cycloaddition of Cyclopentyne towards Enol Ethers

“…Benzyne has a global electrophilicity value of 1.95 eV,25 and it may be classified as a strong electrophile within the electrophilicity scale 22. It undergoes nucleophilic addition reactions 8,9. On the other hand, cyclohexyne has an electrophilicity value of 1.21 eV, which corresponds to a moderate electrophile in the theoretical scale of electrophilicity 22.…”

“…α‐Methoxybenzyne undergoes several regioselective reactions like nucleophilic additions,8,9 [2+4] cycloadditions,10 and [2+2] cycloadditions 11–14. Recently, Suzuki et al15 have reported the [2+2] cycloaddition of the benzyne 9 , which possesses a fused four‐membered ring, with the ketene silyl acetal 10 to yield the cycloadducts 11 and 12 with high regioselectivity (31:1; see Scheme ).…”