Mechanistic insight into the thermal 1,3-chlorine migrations of N-chloroacetanilides under neutral conditions

Diverse and chemoselective sigmatropic shift rearrangements of multisubstituted N,O-diarylhydroxylamines

N,O-Diarylhydroxylamines generally favor the [3,3] sigmatropic shift rearrangement. Possible N/O[1,3] sigmatropic shift rearrangements of multisubstituted N,O-diarylhydroxylamines were investigated experimentally with rationally designed substrates, which were generally in situ prepared from suitable nitroaryl halides and N-arylhydroxylamines via aromatic nucleophilic substitution. The results indicate that both N- and O-(2,4,6-trimethylphenyl)hydroxylamines still favor the [3,3] sigmatropic shift followed by tautomerization rather than N[1,3] and O[1,3] sigmatropic shifts and the rearranged products of N-(2,4,6-trimethylphenyl)hydroxylamines further undergo an intramolecular nucleophilic addition to afford dibenzo[b,d]furan-4a(9bH)-amine derivatives, while N-(4-mono- and 3,5-disubstituted phenyl)-O-(2,4,6-trinitrophenyl)hydroxylamines favorably first undergo the O[1,3] sigmatropic shift followed by tandem Smiles rearrangement and amide/ester exchange reactions, generating 2-arylaminoaryl benzoate derivatives. N-Phenyl-O-(2,4,6-trinitrophenyl)hydroxylamines undergo tandem double O[1,3] sigmatropic shift rearrangement to produce formal O[1,5] shift products. However, O-(2,6-dinitrophenyl)-N-(4-substituted phenyl)hydroxylamines undergo tandem O[1,3] and double [3,3] sigmatropic shift rearrangements to give formal 3,5-shift products. The proposed mechanism is rationalized by density functional theory (DFT) calculations. The current investigation provides not only a comprehensive understanding of the chemoselective sigmatropic shift rearrangements of N,O-diarylhydroxylamines, but also some novel synthetic strategies for dibenzo[b,d]furanamines, diarylamines, diaryl ethers, 2'-amino-[1,1'-biphenyl]-2(1H)-one, and 2'-amino-[1,1'-biaryl]-4-ol derivatives.

Theoretical calculation studies on the rearrangement mechanisms of arenesulfenanilides to generate o- and p-aminodiphenyl sulfides

The thermal and acid-catalyzed rearrangement mechanisms of arenesulfenanilides were investigated theoretically via density functional theory (DFT) calculations. The results indicate that the o-aminodiphenyl sulfide rearrangement involves a novel S[1,3]-sigmatropic shift followed by tautomerization, while the p-aminodiphenyl sulfide rearrangement proceeds via tandem [3,3]- and [3,3]-sigmatropic shifts followed by tautomerization under thermal conditions. Furthermore, computational studies reveal that water assists the proton shift more efficiently than anilines during tautomerization. Moreover, under the acid-catalyzed conditions, the o-aminodiphenyl sulfide rearrangement involves an S[1,3]-sigmatropic shift similar to that under the thermal conditions, while the p-aminodiphenyl sulfide rearrangement proceeds via cascade S[1,3]- and S[1,3]-sigmatropic shifts followed by water-aided tautomerization. The current theoretical studies provide new insights into the formation mechanism of o/p-aminodiphenyl sulfides in the arenesulfenanilide rearrangement and support the unprecedented suprafacial symmetry-allowed S[1,3]-sigmatropic shift with an inversion of the configuration in the migrating sulfur atom. The mechanism is affected by the reaction medium. Disproportionation of arenesulfenanilides into diaryl disulfides and azobenzenes is a competitive radical pathway during the arenesulfenanilide rearrangements.