Abstract
Rearrangements of o-tolyl aryl ethers, amines, and sulfides with the Grubbs–Stoltz reagent (Et3SiH + KOtBu) were recently announced, in which the ethers were converted to o-hydroxydiarylmethanes, while the (o-tol)(Ar)NH amines were transformed into dihydroacridines. Radical mechanisms were proposed, based on prior evidence for triethylsilyl radicals in this reagent system. A detailed computational investigation of the rearrangements of the aryl tolyl ethers now instead supports an anionic Truce–Smiles rearrangement, where the initial benzyl anion can be formed by either of two pathways: (i) direct deprotonation of the tolyl methyl group under basic conditions or (ii) electron transfer to an initially formed benzyl radical. By contrast, the rearrangements of o-tolyl aryl amines depend on the nature of the amine. Secondary amines undergo deprotonation of the N-H followed by a radical rearrangement, to form dihydroacridines, while tertiary amines form both dihydroacridines and diarylmethanes through radical and/or anionic pathways. Overall, this study highlights the competition between the reactive intermediates formed by the Et3SiH/KOtBu system.
Highlights
IntroductionThe first firstaryl arylmigration migration reaction was published by Wieland in [1].[1]. Sincemany The reaction was published by Wieland in 1911 many studies have graced the literature, presenting synthetically useful transformations studies have graced the literature, presenting synthetically useful transformations [2,3]
Subjecting o-tolylaryl ethers and amines to the Et3 SiH/KOt Bu system yields rearranged products. o-Tolylaryl ethers undergo a concerted Truce–Smiles rearrangement to yield diarylmethane products that is initiated by benzyl anions formed by two competitive routes: a radical-polar crossover consisting of a hydrogen atom abstraction by a trialkylsilyl radical 24a followed by a single electron transfer (SET) reduction via silyl radical anion 26a, and/or the direct deprotonation of the ortho methyl group by the pentavalent silicate base that is formed in situ
O-Tolyl arylamines that are secondary, or that contain a labile group bonded to the nitrogen atom, result in the formation of dihydroacridine products through a radical pathway when treated with the Et3 SiH/KOt Bu system
Summary
IntroductionThe first firstaryl arylmigration migration reaction was published by Wieland in [1].[1]. Sincemany The reaction was published by Wieland in 1911 many studies have graced the literature, presenting synthetically useful transformations studies have graced the literature, presenting synthetically useful transformations [2,3]. The first firstaryl arylmigration migration reaction was published by Wieland in [1]. Sincemany The reaction was published by Wieland in 1911 many studies have graced the literature, presenting synthetically useful transformations studies have graced the literature, presenting synthetically useful transformations [2,3]. The. Smiles rearrangement, discovered in 1930 an intramolecular SNAr reaction. Smiles rearrangement, discovered in 1930 [4,5], an [4,5], intramolecular. SN Ar reaction taking taking place at the ipso position of a substituted aromatic system, is an example an aryl place at the ipso position of a substituted aromatic system, is an example of anofaryl mimigration under basic conditions (Scheme [6,7].This ThisSSNAr. Arreaction, reaction, like like the the vicarious vicarious gration under basic conditions 1) 1) [6,7]
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