Cyclohexa-2,4-dien-l-one

Cyclohexadiene 45 was converted to 46 by what has proven to be a general method for preparation of the cyclohexa-2,4-dien-l-one ring system.2 Fragmentation of the aziridinyl imine in 46 at 110 °C gave an intermediate diazoalkane which underwent an intramolecular 1,3-dipolar cycloaddition to give the pyrazoline 47. At 140 °C, pyrazoline 47 expelled N2 and rearranged to the tricyclic ketone 48. The development of this and related bicyclizations29 illustrated a practical synthetic equivalence of an intramolecular diene-carbene 4-1-1 cycloaddition in the cyclohexa-2,4-dien-l-one series. 

Comparison with the reported reactivity of the spiro[2.5]octa-l,4-dien-3-one 110 and 4-(hexafluoroisopropylidene)cyclohexa-2,4-dien-l-one 111 have suggested that the conjugated cyclopropane ring of compounds 108 and 109 imparts a strong acid dependence to its reactivity with nucleophiles, Eq. (45). This property is likely to be relevant for the exceptional reactivity of these antibiotics toward DNA [148]. 

Problem 17.6 C H,OH, an enol, is much more stable than its keto isomer, cyclohexa-2,4-diene-l-one. 

For all practical purposes, the compound cyclohexa 2,4-dien-l One exists totally in its enol form. Write the structure of cyclohexa-2,4-dien-l-one and of its enol form. What special factor accounts for the stability of the enol form ... 

Bis-allylic oxidation of 23 and related cyclohexa-1,4-dienes provides a convenient and general preparation of cyclohexa-2,5-dien-l-ones (Scheme 7). These cross-conjugated die-nones are substrates for a variety of photochemical rearrangement and intramolecular cycloaddition reactions. Amide-directed hydrogenations of dienones 24a and 24b with the homogeneous iridium catalyst afford cyclohexanones 25a and 25b, containing three stereogenic centers on the six-... 

The 1,2-shift of pcrfluoroalkyl groups from carbon to carbon has been reported in an acyloin-like rearrangement of 4-hydroxy-4-(perfluorooctyl)cyclohexa-2,5-dien-l-one (19) to hy-droquinone 20.13... 

Keywords 4-(3-butenyl)cyclohexa-2,5-dien-l-one, inclusion complex, photocy-clization... 

Photoirradiation of inclusion crystals of the 4-(3-butenyl)cyclohexa-2,5-dien-l-ones (83) with the optically active host compounds (12c) in the solid state gave optically active l-carbomethoxytricyclo[4.3.1.0]dec-2-en-4-ones (84). For... 

The desymmetrization of 4-substituted-4-(3-formylpropyl)cyclohexa-2,5-dien-l-one 65 formed - in a single step - three contiguous stereocenters, including a quaternary stereocenter (Scheme 2.56). 

A similar procedure with Bu SiCFj gave 4-(tributyisiloxy)-4-(trifluoromethyl)cyclohexa-2,5-dien-l-one yield 59%. 

Di-ferf-butyl-4-(2,3-diphenylcycloprop-2-enylidene)cyclohexa-2,5-dien-l-one(6, R = f-Bu) Typical Procedure ... 

Parallel to this reaction, an isomerization process of 2,3,4,4,6-pentachloro-cyclohexa-2,5-dien-l-one 2 in pentachlorophenol 1 takes place. 

Reaction with p-benzoquinones.6 Fischer and Henderson have found conditions that result in 1,2-addition of various RLi reagents to p-benzoquinonc. The reaction when conducted in ether at —78° results in 4-alkyl-4-hydroxycyclohexa-2,5-diene-l-ones. These products undergo further 1,2-addition with RLi in THF to give dialkyl-cyclohexa-2,5-diene-l,4-diols. Mixed dienediols can be obtained by use of two different RLi reagents. 

Titrimetric methods take advantage of the redox properties of l-ascorbic acid. Usually, oxidising agents are used to oxidise it to dehydroascorbic acid. A technique which was first introduced as long ago as 1927 utilises the compound 2,6-dichlorophenolindophenol, or 2,6-dichloro-4-[(4-hydroxyphenyl)imino]cyclohexa-3,5-dien-l-one, which is blue at neutral pH and pink in acid solution and which... 

Sodium tetrahydridob orate I sodium hydroxidel irradiation 4-Hydroxyspiro(cyclohexa-2,5-dien-l,F-isoindolin)-3 -ones... 

An aq. soln. of 2-bromo-N-ethyl-4 -hydroxybenzanilide, NaOH, and NaBH4 irradiated 1.25 hrs. with a 100 w. high-pressure Hg-lamp 2 -ethyl-4-hydroxy-spiro(cyclohexa-2,5-diene-l,l -isoindolin)-3 -one. Y 62% based on startg. m. consumed. Z. Horii et al., Chem. Commun. 1970, 1039. 

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