The intermediates in the interaction of phenols with N-bromosuccinimide

Abstract

. 66, 2556 (1988).Phenols react with N-bromosuccinimide to generate 2-bromocyclohexadienone-type intermediates that enolize to 2-bromophenols thermally or photolytically with a wide range of rate constants depending on the parent phenol. A trace amount of acids not only accelerates the rates of the formation and decomposition of the 2-bromodienones, it also promotes the rearrangement of the 2-bromodienones to cross-conjugated 4-bromocyclohexadienones. The enolization of these last compounds affords 4-bromophenols. The occurrence of autocatalysis in dienone decompositions arising from more acidic bromophenols is also established. The reaction is assumed to occur by a bromophilic attack of phenols on the N-Br bond to form unstable hypobromites that rapidly rearrange to the 2-bromocyclohexadienone intermediates. The quantum yield of the photodecomposition of 2-bromo-(2H)-naphthalene-I-one in the vicinity of 365 nm was determined to be unity. YUAN L. CHOW, DA-CHUAN ZHAO et CARL I. JOHANSSON. Can. J. Chem. 66, 2556Chem. 66, (1988.Les ph6nols rCagissent avec le N-bromosuccinimide pour conduire B des intermediaires du type bromo-2 cyclohexadi&nones, qui slCnolisent en bromo-2 phCnols d'une f a~o n thermique ou photochimique et avec des constantes de vitesse trks variables suivant la nature des phtnols de base. L'addition de traces d'acides n'acctlere pas uniquement les vitesses de formation ou de dCcomposition des bromo-2 diknones, elle provoque aussi la transposition des bromo-2 diknones en bromo-4 cyclohexadi&nones avec une conjugaison croiste. L'Cnolisation de ces derniers composCs conduit h des bromo-4 phCnols. On a aussi dCmontrC que des d6compositions des diCnones se produisent sous I'effet d'une autocatalyse qui est die aux bromophCnols qui sont plus acides. On suppose que la rCaction se produit par une attaque bromophile des phtnols sur la liaison N-Br qui conduit h la formation d'hypobromites instables qui se transposent rapidement en intermtdiaires bromo-2 cyclohexadiknones. On a Ctabli que le rendement quantique de la photodCcomposition de la bromo-2 (2H)-naphtalknone-l , autour de 365 nm, est Cgal B un.[Traduit par la revue] N-Bromosuccinimide (NBS) is a versatile brominating agent -mixture immediately revealed a pale yellow colour and rapidly and has been used extensively in radical and ionic brominations developed an absorption peak at 357 nm with two isobestic (1-3).~ We have observed that NBS reacts with phenols in points at 269 and 323 nm (Fig. la). The absorption peak of the aprotic solvent cleanly with second-order kinetics to form new product was confirmed further by a diffe~entialultraviolet unstable intermediates that are shown to have dienone-type spectroscopic method in which the mixture was scanned against structures. The kinetics of formation and the behavior of a reference containing solutions of the starting materials these intermediates are described in this paper. Bromination(1-NpOH and NBS in double concentrations) separately placed of phenols with bromine has been studied extensively a...

Visible‐Light Promoted Catalyst‐Free Imidation of Arenes and Heteroarenes

“…Notably, the reactions with biphenyls occurred exclusively para to the phenyl moiety (the substituted one) ( 3 q and 3 r ) and no other regioisomers were detected. It should also be noted that the current reaction didn′t work well with highly electron‐rich arenes/heteroarenes, such as phenols and anilines 13…”

“…It should also be noted that the current reaction didn't work well with highly electron-rich arenes/heteroarenes, such as phenols and anilines. [13] The catalyst-free imidation reaction has also been tested with heteroarenes. In this regard, N-Boc-pyrrole (tert-butoxycarbonyl) and N-Boc-indoles worked well in the reactions to give the desired adducts in high yields (Scheme 1, 4 a-4 e), although their N-methylated derivatives worked poorly.…”

Efficient Synthesis of a New L-Shaped Dimer of Naphthalene, and Its Analogs

“…Carboxylic acid 10 was prepared by Ullmann ether coupling of 7-methoxy-1-naphthol with isopropyl 8-iodo-1-naphthoate, 4) followed by hydrolysis. Carboxylic acid 11 was prepared by Ullmann ether coupling of 1-naphthol with isopropyl 8-iodo-1-naphthoate, followed by bromination 12) and hydrolysis. closure of 10 afforded 12 selectively, although 10 contains an electron-donating group at the 7 0 position.…”

Regioselective Monobromination of Free and Protected Phenols

“…We chose these two highly polar solvents as it is known that polar solvents drive the bromination reaction through the stabilization of bromocyclohexadienone-type intermediates. [17] DMF [18] as well as MeCN [15] have been described previously as good solvents for nuclear bromination reactions of aromatic systems with NBS. However, the bromination of a polyphenol with NBS in THF has only been reported once, [19] and has only rarely been used for the bromination of monosubstituted methoxy-or benzyloxyanilines.…”