An improved synthesis for dienone 1a and new syntheses for the spirodienones 1b and c are submitted. The dienone phenol rearrangement riaz ahmad department of chemistry, university of agriculture, faisalabad. The aromatic claisen rearrangement is accompanied by a rearomatization. Dienonephenol rearrangement cyclohexadienone derivatives that have two alkyl groups in the 4 position undergo, on acid treatment,1,2 migration of one of these groups from 64 to give the phenol.
Likewise, in for example the pinacol rearrangement. These metrics are regularly updated to reflect usage leading up to the last few days. The experiment is based on the dienone phenol rearrangement reaction of the sesquiterpene santonin to give desmotroposantonin acetate. An improved procedure for the phenoldienone rearrangement of sterically hindered phenols. On the mechanism of the dienonephenol rearrangement of a 2methyl1,4dien3one. Dienonephenol rearrangement of 8,8dimethyl and 6,8,8trimethylnaphthalene 1,4,58htriones 1 and 2 in acetic anhydride as solvent is the subject of a.
The aliphatic claisen rearrangement is a 3,3sigmatropic rearrangement in which an allyl vinyl ether is converted thermally to an unsaturated carbonyl compound. In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of a hydroxyl group o h bonded directly to an aromatic hydrocarbon group. The course of the rearrangement is through one or more 1,2shifts in a benzenonium ion intermediate, and the products are usually phenols or. Dienonephenol rearrangement an overview sciencedirect. Transformation of a 4,4disubstituted cyclohexadienone into a 3,4disubstituted phenol upon acid treatment. The effects of sulphuric and acetic acids are also investigated. Inspection shows that a skeletal change occurs in the following transformation, that is. Dienonephenol rearrangement mechanism of 8,8dimethyl. Re2o7 catalyzed dienonephenol rearrangement the royal. The dienonephenol rearrangement is a useful tool for the synthesis of highly substituted phenols.
A succinct synthesis of the vaulted biaryl ligand vanol. Whereas 1a is stable in trifluoroacetic acid, 1b and c rearrange to form the dienones b and c. Mechanism involves rearrangement of the carbocation intermediate. Dienone phenoltype rearrangement of 4,4disubstituted. The dienonephenol rearrangement of 4,4disubstituted cyclohexadienones catalyzed by re2o7 has been described. For other examples of this reaction, see miller, 1975. Only c is further transformed into the stable final product phenol 16c. Dienone phenol rearrangement of 8,8dimethyl and 6,8,8trimethylnaphthalene 1,4,58htriones 1 and 2 in acetic anhydride as solvent is the subject of a. The dienone phenol rearrangement it is so named, because the sm dienone, and the product phenol. The experiment is based on the dienonephenol rearrangement reaction of the. The organic layers are combined, washed with cold 4 m naoh and brine successively. The mechanism of the dienonephenol rearrangement of 2acetoxy cyclohexadienones. Pdf dienonephenol rearrangement of 4,4disubstituted cyclohexadienones.
During a study of the abnormal dienonephenol rearrangement discovered by marvell and geiszler, imel 1960 found that 4oxo3,3dimethyl3,4dihydrophenanthrene rearranged slowly to a phenol which was tentatively identified as 3,4dimethyllphenanthrol. When pinacol is treated with dilute on moderately concentration sulphuric acid h 2so4, the rearrangement reaction takes place which leads to the formation of ketone called as pinacolone and the rearrangement is known as pinacolpinacolone or pinacolic rearrangement. The experiment is based on the dienonephenol rearrangement reaction of the sesquiterpene santonin to give. A comprehensive laboratory experiment for advanced undergraduate organic chemistry students. In our previous study of the rearrangement of 4,4disubstituted 2hydroxycyclohexa2,5 dienone. Acidpromoted rearrangement of 4,4disubstituted cyclohexadienones to 3,4disubstituted phenols. Note that in some instances, for example the beckmann rearrangement, only one group ever migrates regardless of the aptitude, simply because of stereoelectronic requirements for the reaction. Phenolic compounds are classified as simple phenols or polyphenols based on the number of phenol units in the molecule. The driving force for this reaction is the formation of aromatic rings ch423courseonorganicsynthesis. This process is experimental and the keywords may be updated as the learning algorithm improves. Received november 23, 1985 abstract the influence of the reaction medium on the course of the dienone phenol re arrangement of cholestal, and cholestal, 4, was investigated. In the acidcatalyzed dienonephenol rearrangement of 7 and 8, the c4 substituent migrates regioselectively to c5, completely shunning the enol double bond, even though the substituents at. Bromination of phenols, isomerization and disproportionation of bromophenols, and dienonephenol rearrangement of bromodienones.
In our previous study of the rearrangement of 4,4disubstituted 2hydroxycyclohexa2,5dienone under deoxyfluorination conditions, bond migration proceeded with very poor regioselectivity. The etherification of alcohols or phenols and their subsequent claisen rearrangement under thermal conditions. The experiment is based on the dienonephenol rearrangement reaction of the sesquiterpene santonin to give desmotroposantonin acetate. Write step bystep mechanisms for the following transformations. Citations are the number of other articles citing this article, calculated by crossref and updated daily. Supporting information for re2o7 catalyzed dienonephenol rearrangement zilei xia,a,b. Novel dienonephenol type rearrangement of 4,4disubstituted cyclohexadienone system using thiosilane yasufumi wada, kouji otani, noriko endo, yasuyuki kita and hiromichi fujioka. The dienone phenol rearrangement is a useful tool for the synthesis of highly substituted phenols. Possible paths for the alpha blocked dienonephenol. Regioselective rearrangement of 4,4disubstituted 2. Oxidation with can under optimized conditions let to conversion of 48 into the spirocyclicquinone in 76% yield, which was followed by dienonephenol rearrangement using ticl 4. These keywords were added by machine and not by the authors.
Possible paths for the alpha blocked dienonephenol rearrangement. The dienonephenol rearrangement journal of the american. A phosphorylation of steroids and a dienonephenol rearrangement leading to a secosteroidal aldehyde which has a strong toxicity. It challenges students to solve an earlier controversial stereochemical problem. An energetic requirement is also observed in order for a rearrangement to take place. The dienonephenol rearrangement is so named because the starting material is a dienone and the product is a phenol. Note that a photochemical version of this reaction has been observed dr. Phenol rearrangement of spirooxetanes from photoaddition of quinones with electron donor olefins. A particularly useful example of dienonephenol rearrangement can be found in the. Rearrangement of semibenzenes into alkylben zenes has been studied in some detail by v.
Download pdf 1280k download meta ris compatible with endnote, reference manager, procite, refworks. A carbocation is a trivalent, positively charged carbon atom. These metrics are regularly updated to reflect usage leading up to the last few. Reactions rearrangements and reagents download ebook pdf. Article views are the countercompliant sum of full text article downloads since november 2008 both pdf and html across all institutions and individuals. Both substrates show limiting hso dependence and an inhibiting effect with ace. Dienonephenol rearrangement of 8,8dimethyl and 6,8,8trimethylnaphthalene1,4,58triones and in acetic anhydride as solvent is the subject of a kinetic study. Benzil benzilic acid rearrangement problems with solution iit jam ugc csir net set gate chemistry duration. Pdf a comprehensive laboratory experiment suitable for advanced undergraduate organic chemistry students has been designed. This site is like a library, use search box in the widget to get ebook that you want. The dienonephenol rearrangement a substituted dienone may undergo rearrangement and aromatization of the dienone ring in acid solutions. Click download or read online button to get reactions rearrangements and reagents book now. A comprehensive laboratory experiment suitable for advanced undergraduate organic chemistry students has been designed. On the mechanism of the dienonephenol rearrangement of a.
217 1248 1112 643 386 346 265 785 86 1199 454 1399 447 290 383 853 1298 1368 383 1318 1330 1048 147 983 574 127 653 1334 274 1576 1511 221 918 715 350 874 857 789 1129 1241 933