- Intermediacy of o-sulfonylium arenide ylides in the reactions of arenesulfonyl derivatives with strong bases: Insight into the puzzling rearrangement of N-arylarenesulfonamides into 2-aminodiaryl sulfones
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Benzenesulfonyl derivatives, PhSO2E, such as benzenesulfonyl fluoride, phenyl benzenesulfonate, and N-methyl-N-phenylbenzenesulfonamide, have been found to undergo ortho-lithiation with lithium 2,2,6,6-tetramethylpiperidide (LTMP) in THF at -78 °C. The resulting lithio derivatives undergo 1,3-elimination of LiE to form the transient o-sulfonylium benzenide. The latter ylide, which may be stabilized by its carbenoid character and its complexation with LiE, can be trapped by benzophenone acting as a 1,3-dipolarophile to form the adduct, 3,3-diphenyl-1,2-benzoxathiole 1,1-dioxide. The alternative formation of the latter cyclic sulfonate by reaction of the initially formed o-lithio derivative with benzophenone and by subsequent cyclization was shown not to occur. If not trapped with benzophenone, such an ylide decomposes partly into SO2 and benzyne and then undergoes self-condensation to yield poly(phenylene-o,o′-biphenylene sulfones). o-Sulfonylium benzenide also can be captured by lithium alkoxides, either present adventitously or intentionally added, to generate the corresponding alkyl benzenesulfonate. However, such alkoxides, unaided by LTMP, are themselves unable to extract an ortho-proton from benzenesulfonyl fluoride or from N-methyl-N-phenylbenzenesulfonamide to yield the corresponding o-lithio derivative. With benzenesulfonyl fluoride the lithium alkoxide can also form the sulfonate ester by direct substitution at the sulfonyl group. The Closson-Hellwinkel rearrangement of N-methyl-N-phenylbenzenesulfonamide into o-(methylamino)diphenyl sulfone by RLi or LTMP is reinterpreted as proceeding by way of the 2-lithio- or 2,6-dilithiobenzenesulfonyl derivative which eliminates lithium N-methylanilide to form the o-sulfonylium benzenide or its 6-lithio derivative. Attack of the latter ylide, acting as an electrophile, upon the ortho-position of the presumably complexed LiNMePh then consummates the rearrangement.
- Eisch, John J.,Qian, Yun,Chiu, Chingchen S.
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p. 1392 - 1398
(2007/10/03)
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- Acid-catalyzed hydrolysis of benzenesulfonamides. Rate enhancements by ortho-alkyl substituents
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Pseudo-first-order rate constants have been measured for the acid-catalyzed hydrolysis of a series of N,N-dimethyl- and N-methyl-N-phenylbenzenesulfonamides in 70 percent (v/v) CF3CO2H/H2O at 99 deg C.Analysis of the effect of the alkyl substituents in the benzene ring shows a remarkable rate enhancement by ortho-alkyl groups, in the contrast with a rate retardation of similar substituents in the corresponding benzamides.The rate enhancement in the sulfonamides is attributed to relief of initalstate strain in the transition state for hydrolysis.When the sulfonamide moiety is contained in a five-membered ring fused to a phenyl ring, the rate of hydrolysis is markedly reduced by an ortho-methyl substituent.
- Wagenaar, Anno,Kirby, Anthony J.,Engberts, Jan B. F. N.
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p. 203 - 205
(2007/10/02)
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