Cyclohexadienones, substituted, preparation

Cyclohexadienones, substituted, preparation of, 46,119 reactions of, 46,119 Cyclohexane from reduction of chloro-cyclohexane, 47,105 A -o-Cyclohexaneacetic acid, ethyl ESTER, 45, 44... 

Iron pentacarbonyl and l-methoxy-l,4-cyclohexadiene react as shown by Birch and oo-workera, but in dibutyl ether this solvent has been found superior. The tricarbonyl(methoxy-l,3-cyclohexadiene)iron isomers undergo hydride abstraction with triphenylmethyl tetrafluoro-borate to form the dienyl salt mixture of which the 1-methoxy isomer is hydrolyzed by water to the cyclohexadienone complex. The 2-methoxy isomer can be recovered by precipitation as the hexafluoro-phosphate salt. By this method the 3-methyl-substituted dienone complex has also been prepared from l-methoxy-3-methylbenzene. The use of the conjugated 1-methoxy-1,3-cyclohexadiene in Part B led to no increase in yield or rate and resulted chiefly in another product of higher molecular weight. An alternative procedure for the dienone is to react tricarbonyl(l,4-dimethoxycyclohexadiene)iron with sulfuric acid. ... 

This preparation of 2,6,6-trimethyl-2,4-cyclohexadienone is based upon the published procedure of the submitters,2 and it is the only preparation of the 2-substituted-2,4-cyclohexadienones. The simpler 6,6-dimethyl-2,4-cyclohexadienone is more conveniently prepared by the method of Alder.4... 

The alkylation procedure can be used to prepare a wide variety of 2-substituted-2,4-cyclohexadienones, 2,3 5i 6 which are useful starting materials. The compounds can serve either as dienes or dienophiles7 in the Diels-Alder reaction and can be opened photochemically to yield substituted A3,5-hexadienoic acids.8... 

The phenol-dienones could be conveniently prepared directly from phenols by reaction with Br2 in the presence of AgC104 and Na2C03. These dienones are transformed efficiently to the 4-alkoxycyclohexa-2,5-dienones by the silver ion mediated reaction in the presence of the corresponding alcohols (equation 96) 48s solid-phase bromina-tion of ferf-butyl-substituted phenols with N-bromosuccinimide also affords halogenated cyclohexadienones . ... 

Cycloaddition. The reagent has been used in Diels-Alder reactions to prepare 4-acyl-4-substituted cyclohexadienones after selenoxide elimination. Examples ... 

In principle, cyclohexadienones can be accessed through tautomerization of the corresponding phenol. However, the loss of aromatic stabilization makes this impractical in all but the most specialized of cases. In order to access an isolable cyclohexadienone, the aromaticity of the phenol must be destroyed. One way to do this is through C-alkylation, but this is mostly limited to intramolecular electrophiles. Oxidative dearomatization of the phenol is by far the most conunon method used to prepare both 2,4- and 2,5-cyclohexadienones. A variety of oxidants can be used for this transforma-tiOTi, but iodine(III)- and iodine(V)-based oxidants" have emerged as the reagents of choice in many cases. An attractive feature of these oxidants, especially those based on iodine(III), is that they can be used with a variety of different nucleophiles, thereby providing access to cyclohexadienones with different substitutents. 

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