Reactions of some halogenocyclohexadienones

Abstract

Chlorination of 2,4-, 2,6- and 3,5-di-t-butylphenols gave the chlorocyclohexa-dienones (2a), (10), and (7) and (9), respectively. Base-catalysed methanolysis of the ketones (2a) and (9) produced the rearranged gem-dimethoxycyclohexadienones (5)and (11). Under similar conditions the ketone (7) rearranged to 3,5-di-t-butyl-2,4- dichlorophenol, while (10) was converted into a mixture of 2,6-di-t-butyl-1,4-benzo-quinone and 3,5,3',5'-tetra-t-butyl-4,4'-diphenoquinone. The dibromocyclohexa-dienone (2b) also dimerized in the presence of base, affording a low yield of 2,2'-dihydroxy-3,5,3',5'-tetra-t-butylbiphenyl. The mechanisms of these reactions are discussed.

Chlorination of 3,5-Di-tert-butylphenol+ Crystal Structure of the Keto Tautomer of a Sterically Hindered Phenol

“…The product obtained on chlorination of 3,5-direrr-butylphenol with 1 -chlorobenzotriazole was identical in every respect (m .p., IR, UV, 'H NMR, MS) to that reported by Hewitt et al [10]. Minor Table II According to the general rules for the discrimina tion of ortho-and /?ara-quinolide structures [2,17], UV (Amax = 257 nm, log e = 4.07) and IR spectra [vco = 1665 (Nujol), 1657 (KBr)] would be better compatible with thepora-quinolide structure l a .…”

“…H itherto, assuming structure 2a instead of l a for the keto form, a more complicated rearrangem ent involving ortho -* para migration of a chlorine atom was inevitable to ex plain the form ation of 3 [10]. Such a reaction, al though possible (vide infra), is however unlikely under the experim ental conditions used (R .T ., 1 h).…”

“…Con sidering only monocyclic compounds, terf-butylated species 2 were particularly attractive, since the tertbutyl groups are expected to stabilize quinol halides in general [9]. Of the six possible di-rm -butylated 6,6-dichloro-2,4-cyclohexadien-l-ones only 2 a has been reported [10] and was chosen for the 13C NMR m easurem ents m entioned above. IR, UV and NMR spectra, however, were not in full agreem ent with the proposed structure but admitted of the paraquinol structure l a as well.…”

“…89-90 °C (lit. [10] (5 ml) and N aO H (0.1 g) and stirred at room tem perature for 1 h. Afterwards, the mixture was acidified with citric acid (5% aqueous solution) and extracted with ether ( 1 0 ml) to give 140 mg (70% ) of crude 3, which was purified by pre parative TLC [petroleum ether (b.p. 60-90 °C)/ C H 2C12 1:1 (v:v)].…”

“…IR, UV and NMR spectra, however, were not in full agreem ent with the proposed structure but admitted of the paraquinol structure l a as well. This would then be one of the rare cases where the keto tautom er of a monocyclic phenol (3) exists at room tem perature [10][11][12]. T herefore, and in order to settle the struc tural problem finally, a crystal structure determ ina tion was perform ed which decided in favour of struc ture l a .…”