INTERMEDIACY OF O-SULFOLLYLIUM ARENIDE YLIDES IN THE REACTIONS OF ARENESULFONYL DERIVATIVES WITH STRONG BASES - INSIGHT INTO THE PUZZLING REARRANGEMENT OF N-ARYLARENESULFONAMIDES INTO 2-AMINODIARYL SULFONES

Benzenesulfonyl derivatives, PhSO(2)E, such as benzenesulfonyl fluorid e, phenyl benzenesulfonate, and N-methyl-N-phenylbenzenesulfonamide, h ave been found to undergo ortho-lithiation with lithium 2,2,6,6-tetram ethylpiperidide (LTMP) in THF at -78 degrees C. The resulting lithio d erivatives undergo 1,3-elimination of LiE to form the transient o-sulf onylium benzenide. The latter ylide, which may be stabilized by its ca rbenoid character and its complexation with LiE, can be trapped by ben zophenone acting as a 1,3-dipolarophile to form the adduct, 3,3-diphen yl-1,2-benzoxathiole 1,1-dioxide. The alternative formation of the lat ter cyclic sulfonate by reaction of the initially formed o-lithio deri vative with benzophenone and by subsequent cyclization was shown not t o occur. If not trapped with benzophenone, such an ylide decomposes pa rtly into SO2 and benzyne and then undergoes self-condensation to yiel d poly(phenylene-o,o'-biphenylene sulfones), o-Sulfonylium benzenide a lso can be captured by lithium alkoxides, either present adventitously or intentionally added, to generate the corresponding alkyl benzenesu lfonate. However, such alkoxides, unaided by LTMP, are themselves unab le 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 als o form the sulfonate ester by direct substitution at the sulfonyl grou p. The Closson-Hellwinkel rearrangement of N-methyl-N-phenylbenzenesul fonamide into o-(methylamino)diphenyl sulfone by RLi or LTMP is reinte rpreted as proceeding by way of the 2-lithio- or 2,6-dilithiobenzenesu lfonyl derivative which eliminates lithium N-methylanilide to form the o-sulfonylium benzenide or its 6-lithio derivative. Attack of the lat ter ylide, acting as an electrophile, upon the ortho-position of the p resumably complexed LiNMePh then consummates the rearrangement.