Friedel-Crafts reaction epoxides

Friedel-Crafts. 2-Phenylpropanol results from the catalytic (AlCl, FeCl, or TiCl reaction of ben2ene and propylene oxide at low temperature and under anhydrous conditions (see Friedel-CRAFTS reactions). Epoxide reaction with toluene gives a mixture of 0-, m- and -isomers (75,76). 

Another type of soHd supetacid is based on perfluorinated resin sulfonic acid such as the acid form of Du Font s Nafion resin, a copolymer of a perfluorinated epoxide and vinylsulfonic acid or soHd, high molecular weight petfluotoalkanesulfonic acids such as petfluotodecanesulfonic acid, CF2(CF2)qS02H. Such sohd catalysts have been found efficient in many alkylations of aromatic hydrocarbons (225) and other Friedel-Crafts reactions (226). 

Further dechlorination may occur with the formation of substituted diphenyhnethanes. If enough aluminum metal is present, the Friedel-Crafts reactions involved may generate considerable heat and smoke and substantial amounts of hydrogen chloride, which reacts with more aluminum metal, rapidly forming AlCl. The addition of an epoxide inhibits the initiation of this reaction by consuming HCl. Alkali, alkaline-earth, magnesium, and zinc metals also present a potential reactivity hazard with chlorinated solvents such as methylene chloride. 

Asymmetric microbial oxidation afforded the (-)-epoxide which has been explored as a building block ring opening reactions with organometallic nucleophiles, and via Friedel-Crafts reactions have been reported. [226,227]. A non-biotransformative approach to this epoxide has also been described [228]. Copper(II)-catalysed oxidative hydrolysis (Eq. 72) affords a lactic acid analogue in high enantiomeric purity [229]. 

Epoxides have occasionally been used in Friedel-Crafts reactions, and some interesting stereochemical observations have been made in this context. Quite unlike secondary alcohols which give almost fully racemized product, it has been shown that optically pure propylene oxide with AlCh and benzene gives optically pure 2-phenyl-1-propanol with inversion of configuration at the cleaved center. AlBrs leads to much lower levels of optical purity it was demonstrated that both starting material and product are optically stable to the reaction conditions, and therefore partial racemization is intrinsic to the mechanism with AlBrs. It is nonetheless clear from these and other results that even powerful Lewis acids do not assure reaction via simple planar carbenium ions. 

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