4-Chromanols

4 VO(acac)2/TBHP CATALYZED EPOXIDATION OF 2-(2-ALKENYL)PHENOLS. HIGHLY REGIO- AND DIASTEREOSELECTIVE OXIDATIVE CYCLIZATION TO 2,3-DIHYDROBENZOFURANOLS AND 3-CHROMANOLS 

Dipartimento di Chimica, Universitd di Salerno, 84081 Baronissi, Italy 

Reprinted from reference [2], with permission from Georg Thieme Verlag KG. 

Entry R R Time (h) Yield 3 % Yield 4 % Diasteromeric ratio 

1 VO(acac)2/TBHP CATALYZED EPOXIDATION OE 2-(3,7-DIMETHYL-0CTA-2,6-DIENYL)-PHEN0L  

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An interesting intramolecular Friedel-Crafts-type cyclization was developed by Pericas et al. Thus, aryl glycidyl ethers reacted to 3-chromanols as the only reaction product when treated with a catalytic amount of FeBr3 in the presence of AgOTf in CH2CI2 at room temperature (Scheme 9) [26]. The addition of a silver salt proved to... 

Scheme 9 Iron(III) bromide-mediated cyclization of aryl glycidyl ethers to 3-chromanols...

Chromanol 4 and 2,3-dihydro-benzofuranol 3 were isolated from the crude reaction mixture by column chromatography (petrol/Et20 90/10-80/20). 3-Chromanol 4 (172.2 mg, 70% yield). 

A gold-catalysed alkylation of arenes with epoxides has also recently been discovered treating phenoxymethyloxiranes with AuCl3/3AgOTf (Tf = CF3SO2- triflate is trifluoromethanesulfonate i.e. OTf) (2.5 mol) in dichloromethane at 323 K yielded exclusively endo addition product 3-chromanols in good yield in 3h 37... 

Treatment of certain allyl aryl ethers with thallium(iu) sulphate in 2.0— 2.5M sulphuric acid gives a direct route to 3-chromanols (266). The... 

Later, He and coworkers developed a new gold(III)-catalyzed stereospecific cycloalkylation of electron-rich arenes with tethered epoxides 23, which provided a rapid access to 3-chromanols 24 (Scheme 12.11) [15]. The proposed reaction mechanism proceeds through C-H activation of the arene, followed by addition to the tethered epoxide (path A) however, a second possible mechanism in which... 

Scheme 12.12 Two possible mechanisms for Au-catalyzed synthesis of 3-chromanol from epoxides 23.

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