Unsaturated phenols

Chavicol, C<,H ( 0, is an unsaturated phenol, found in oils of betel nut and bay leaves. It is a colourless, highly odorous liquid, having the following characters —... 

Hydrogenation of the carbon-carbon double bond occurs without alteration of the ester function when citronellyl acetate is treated with 2.5 equivalents of trifluoroacetic acid and two equivalents of triethylsilane in 2-nitropropane.205 The reduced product is obtained in 90% yield after 22 hours at room temperature in the presence of one equivalent of added lithium perchlorate (Eq. 82). The yields are lower in the absence of this added salt. Similar reduction of an unsaturated phenolic chroman derivative occurs to give an 85% yield of product with only the carbon-carbon double bond reduced (Eq. 83).205... 

Fluorinated unsaturated alcohols have been prepared from the point of view of potential fluo-rinated monomers with a reactive pendant group. There seem to be no examples of the preparation of fluorinated unsaturated phenols by dehalogenation. Examples of the formation of fluorinated unsaturated alcohols are listed in Table 7. 

Although diastereoselective intramolecular al-koxypalladations have been investigated intensively and have found application in synthesis (see above), there are few examples of enantioselective alkoxypalladations [2bJ. For instance, Hosokawa et al. were able to cyclize unsaturated phenol derivatives of type 62 in the presence of chiral (// -allyl-PdOAc complexes, i.e. 63), but only with modest enantioselectivities. Under the same conditions the conversion of the phenol 65 to chroman 66 (a compound related to vitamin E) proceeded in acceptable yields, but with only low asymmetric induction. Newer results by Uozumi et al., for instance the Pd-catalyzed cyclization of 67 to 68 in the presence of a chiral bis-oxazolin ligand [15], show that much higher enantioselectivities can be achieved, at least for certain substrates. 

With 3,5-dimethoxybenzoyl chloride used in the monoacylation of cyclohexanone to produce finally the same (MeO ArC synthon, an alternative synthesis of cardol 8(Z)-monene was developed [138]. Fig( 4)-49, Persoonol dimethyl ether (5-[(Z)-undec-3-enyl]resorcinol dimethyl ether) was synthesised from 3,5-dimethoxybenzyl alcohol [149], This same reactant has been employed for a range of 5-substituted resorcinols although its application to unsaturated phenolic lipids was not discussed [228]. Acetylenic methods have proved valuable for deriving phenolic lipidic double bonds in the Z-configurations and with advances in boration methodology [229] the corresponding E-isomers are accessible. 

The Wittig reaction approach provides an alternative route to the synthesis of the unsaturated phenolic lipids in urushiol in Rhus vernicifera, which contains three C15 isomeric trienes, the major constituent the semi-conjugated Fig (3)-4, 8(Z),11(E),13(Z), (55.4%), the trace corresponding 13(E) isomer (1.7%) and the non-conjugated Fig (3)-5, 8(Z), 11(E), 14 (7.4%) which is also the chief component in urushiol from Rhus toxicodendron. Scheme 1 shows the routes to the first and last constituents [230-233]. 

Wittig reactions then afforded the unsaturated phenolic lipids after demethylation and alkaline hydrolysis as depicted in Schemes 5b and c. 

In Chapter 6 the use of isoprene (Table 6.1) and of geranyl halides in reactions with naphthol and phenol respectively has been briefly referred to. In early work, isoprene with phenol in toluene containing 71% phosphoric acid, when reacted over 16 hours at ambient temperature (ref. 2) gave 4-(3-methylbut-2-enyl)phenol, the corresponding 2- isomer and 4-(3-methyl-3-hydroxybutyl)phenol in the phenolic products and in the neutral fraction, smaller proportions of 2,2-dimethylchroman and 6-(3-hydroxyisopentyl)-2,2-dimethylchroman. Hydrogenation of the unsaturated phenols afforded the respective 4- and 2-isopentylphenols. 

Other epoxy resins are also being manufactured, but their commercial j utilization is not so far advanced as those based on bisphenol A and i epichlorohydrin. For instance, resorcinol and a mixture of diphenol-poly-(hydroxyphenyl)-pentadecanes, obtained by the addition reaction of phenol with an unsaturated phenol derived from cashew-nut oil (see structure below) can be reacted with epichlorohydrin to produce epoxy resins. ... 

Rhus vernicifera n. C22H31O3. Chinese tree which delivers a milky type of liquid. When the water is removed, a dark oily liquid is obtained, which yields a tough flexible film on atmospheric oxidation. The chief constituent of the film-forming material is an unsaturated phenol-acid-urushiol. The liquid is used for the preparation of Japanese lacquer. 

The unsaturated phenol is highly reactive and gives rise to coloured products. This decomposition may be repressed by the use of a molar excess of diphenyl carbonate in the ester interchange reaction. In this way, initial esterification and consequent stabilization of the bisphenol A occurs more rapidly. When an excess of diphenyl carbonate is used, the initial products are low molecular weight polycarbonate chains terminated with phenyl carbonate groups. When these low molecular weight polymers are heated above 250°C under... 

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