Acid-catalysed rearrangements of 4-hydroxycyclohexa-2,5-dienones

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dc.contributor.advisor Woodgate, P.D. en Gash, Diana Mary en 2007-08-29T07:01:37Z en 2007-08-29T07:01:37Z en 1980 en
dc.identifier THESIS 80-151 en
dc.identifier.citation Thesis (PhD--Chemistry)--University of Auckland, 1980 en
dc.identifier.uri en
dc.description Full text is available to authenticated members of The University of Auckland only. en
dc.description.abstract A series of 4-aryl-4-hydroxycyclohexa-2,5-dienones has been synthesised along with one example of a 4-alkyl-4-hydroxycyclohexa-2,5-dienone. The acid-catalysed rearrangements of these compounds have been studied by product analysis. Rearrangement of the 2,6-di-t-butyl-4-aryl-4-hydroxycyclohexa-2,5-dienones (102), (103) and (123) in acetic anhydride-sulphuric acid, Thiele conditions) gave the ortho diacetates (163), (177), and (164), respectively. The formation of these products can be rationalised in terms of a mechanism involving an intermediate phenoxylium ion (193) generated by protonation of the hydroxy oxygen atom of the starting material followed by loss of water (Scheme XIX). In contrast, Thiele rearrangement of the 2,6-dimethyl- and 2,6-di-isopropyl-substituted compounds (124) and (125) afforded the meta diacetates (200) and (202), respectively. The mechanism accepted generally for dienone-phenol rearrangement of 4-hydroxycyclohexa-2,5-dienones (Scheme III) involving protonation of the carbonyl oxygen atom followed by 1,2-migration of a 4-substituent and deprotonation to give an aromatic product, explains the origin of the meta diacetates (200) and (202). The 4-hydroxy-4-methylcyclohexa-2,6-dienone (110d) gave the benzylic diacetate (208) under the same conditions. The rearrangement of 2,6-di-t-butyl-4-hydroxy-4-phenylcyclohexa-2,5-dienone (102) in boron trifluoride diethyl etherate-diethyl ether yielded the biphenylol (104), the benzo-1,3-dioxole (231) and the 4-(2-methylpropenyl)-4-phenylcyclohexa-2,5-dienone (226). In the same medium, rearrangement of 2,6-di-t-butyl-4-hydroxy-4-methylcyclohexa-2,5-dienone (110d) gave a dimeric product (229). The biphenylol (104) and the -o-benzoquinone (187) were the products of rearrangement of 4-hydroxycyclohexa-2,5-dienone (102) catalysed either by aqueous perchloric acid or by trifluoromethanesulphonic acid. The 4-methyl- substituted compound (110d) gave the dimers (269), (273), and (278), as well as the benzyl alcohol (272) when its rearrangement was catalysed by aqueous perchloric acid. The polymeric perfluorosulphonic acid resin, Nafion-H was found to catalyse the rearrangement of the 4-hydroxycyclohexa-2,5-dienone (110d), the products isolated, (269), (273), (278), and (272), being identical to those obtained from the aqueous perchloric acid-catalysed rearrangement of (110d). en
dc.language.iso en en
dc.publisher ResearchSpace@Auckland en
dc.relation.ispartof PhD Thesis - University of Auckland en
dc.relation.isreferencedby UoA9921876214002091 en
dc.rights Restricted Item. Available to authenticated members of The University of Auckland. en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. en
dc.rights.uri en
dc.title Acid-catalysed rearrangements of 4-hydroxycyclohexa-2,5-dienones en
dc.type Thesis en Chemistry en The University of Auckland en Doctoral en PhD en
dc.rights.holder Copyright: The author en

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