Zur thermischen umlagerung von O-arylsulfonyl-N-phenylhydroxylaminen

Rearrangement of Differentially Protected N‐Arylhydroxylamines

“…We therefore examined the introduction of a sulfonyl group on the hydroxylamine oxygen with the hope of facilitating the overall rearrangement process further in agreement with previous reports of this class of transformation (Table 2). 10 To our delight, treatment of the N ‐protected hydroxylamines 7 and 20 – 22 13 with one equivalent of methanesulfonyl chloride and triethylamine at room temperature for 30 min led directly to the rearranged products 23 – 26 in 78–94 % isolated yield (Entries 1–4), providing significantly improved reaction conditions for the sequence. Both carbamate (Entries 1 and 2) and sulfonamide (Entries 3 and 4) were well tolerated on the hydroxylamine nitrogen without compromise in reactivity.…”

“…Subsequent mechanistic studies have shown these reactions proceed via either a [3,3]‐sigmatropic rearrangement process or an ion‐pair mechanism depending upon the reaction conditions adopted 8. In contrast, the related rearrangement of N ‐aryl‐ N ‐sulfonyl‐ O ‐acylhydroxylamines 2 to give 5 9 and N ‐aryl‐ N ‐acyl‐ O ‐sulfonylhydroxylamines 3 to the 2‐functionalised products 6 10 have been shown to proceed exclusively through a concerted pericyclic process. These overall reactions provide a simple and easily accessible method with which to functionalise anilines at the ortho position.…”

Synthesis of Halogenated Anilines by Treatment of N,N-Dialkylaniline N-Oxides with Thionyl Halides

“…We have a longstanding interest in the manipulations of anilines at elevated oxidation levels (Scheme 1). 8 The functionalization of anilines by group transfer is known at the N -arylhydroxylamine oxidation level (Scheme 1, eqs 1 and 2), 9 and a small number of examples of ortho -chlorination reactions have been reported on that platform (Scheme 1, eq3). 10 We report here the practical and convenient syntheses of 2-chloro- N , N -dialkylanilines and 4-bromo- N , N -dialkylanilines as part of our ongoing interests in the reactivity of aniline N -oxides (Scheme 1, eq 4).…”

“…However, the elevated reactivity of aniline N -oxides comes at the cost of mechanistic ambiguity. The manipulations described above employing N -arylhydroxylamines almost certainly proceed by [3,3]-sigma-tropic rearrangement pathways; 9–11 however, reactions with aniline N -oxides may proceed by multiple mechanisms. While the 2-haloaniline products are consistent with a sigmatropic rearrangement, the 4-haloaniline products must arise by a radical pathway or a nucleophilic aromatic substitution-type mechanism.…”

Cationic cobalt-catalyzed [1,3]-rearrangement of N-alkoxycarbonyloxyanilines

“…However, there is a significant drawback, these [3,3]-rearrangements of carboxylic acyloxy and alkoxylcarbonyloxy groups generally require long heating times at elevated reaction temperatures (>140 °C) or microwave irradiation ( Scheme 2 ). In contrast, N -sulfonyloxyanilines are known to readily undergo the [3,3]-rearrangement during the preparation of the starting material below −20 °C due to the strongly electron-withdrawing nature of the sulfonyl group ( Scheme 2 ) [ 12 ]. Accordingly, we envisioned that appropriate Lewis acidic metal catalysts would promote the rearrangement reaction of stable N -acyloxyanilines to afford readily deprotectable 2-acyloxyanilines under much milder reaction conditions with high functional group tolerance.…”