Allyl alcohols Friedel-Crafts reaction

Ionic routes to allylic (2) and benzylic (4) alcohols use reduction of carbonyl compounds (1) and (3) since these are readily available by condensation or Friedel-Crafts reaction. 

Friedel-Crafts reaction of aUyl alcohol with benzene or alkjibenzene yields many kinds of products, in which the reaction species and the product ratio depend on the type of catalyst. Zinc chloride is the most effective catalyst for producing allyl compounds by this reaction (32). 

Friedel-Crafts reactions. Alkylation of arenes with benzylic and allylic alcohols is achieved with Sc(OT03 as catalyst. An interesting variant is the reductive benzylation using arenecarbaldehydes and l,3-propanediol. The diol serves as a reductant. 

MBH alcohols as electrophiles in a Friedel-Crafts reaction with benzene was initially reported by Foucaud et al., leading to allylic rearrangement products 91 in the presence of KIO montmorillonite. With phenols and ZnBr2-Si02 as catalyst, coumarin derivatives 92 were formed in moderate yields (Scheme 3.28). ... 

Iron salts have recently attracted considerable attention as inexpensive and environmentally friendly agents in a wide range of selective processes in organic synthesis. Over the past decade, FeCls 6H2O has shown to be an effective catalyst in the formation of carbon-carbon or carbon-nitrogen bonds, in intramolecular Friedel-Craft reactions and in the reduction of ketones or allylic alcohols. ... 

Furthermore, Jana et al. developed a FeCl3-catalyzed C3-selective Friedel-Crafts alkylation of indoles, using allylic, benzylic, and propargylic alcohols in nitromethane as solvent at room temperature. This method can also be used for the alkylation of pyrrole (Scheme 4). The reactions were complete within 2-3 h without the need of an inert gas atmosphere leading to the C-3-substitution product exclusively in moderate to good yields [20]. 

A fourfold anionic sequence which is not initiated by a Michael but an aldol reaction has been reported by the group of Suginome and Ito (Scheme 2.129) [295]. In this approach, the borylallylsilane 2-573 reacts selectively in the presence of TiCl4 with two different aldehydes which are added sequentially to the reaction mixture. First, a Lewis acid-mediated allylation of the aldehyde with 2-573 takes place to form a homoallylic alcohol which reacts with the second aldehyde under formation of the oxenium ion 2-574. The sequence is terminated by a Prins-type cyclization of 2-574 and an intramolecular Friedel-Crafts alkylation of the intermediate 2-575 with formation of the fraws-1,2-be rizoxadeca lines 2-576 as single diastereomers. 

The first systematic investigations of the catalytic Friedel-Crafts-type reaction with alcohols and olefines were performed by Yamamoto and colleagues. After reporting the development of a Pd-catalyzed method for the allylation of different naphthol derivatives [24], the authors used Mo(CO)g for the Friedel-Crafts-type alkylation of electron-rich arenes with allyl acetates [25], The same molybdenum catalyst was additionally used for a Friedel-Crafts-type alkylation of arenes using 1-phenylethanol and styrene as alkylating reagents [26], However, Mo(CO)g is toxic and must be handled under strictly inert conditions. Thus, more stable Lewis acids were necessary. 

With Friedel-Crafts halides (usually A1C13 and BF3) it is necessary to use equimolar or excess catalyst when alcohols are the alkylating agents. With primary alcohols usually 2 mol of catalyst per mole of alcohol must be used. Complexing the alcohol, as well as binding the water formed in the reaction explains the experimental findings. With secondary and tertiary alcohols, lesser amounts of catalyst are needed. The reactivity of different alcohols follows the order methyl < primary < secondary < tertiary, allyl, benzyl. The ease of carbocation formation according to Eq. (5.51) is most probably responsible for this reactivity order ... 

Ionic routes to allylic 4 and benzylic 6 alcohols include reduction of the ketones 3 and 5 as these are easily made by aldol reactions and Friedel-Crafts acylation. The alcohols can be converted into electrophiles by tosylation or conversion into bromides. 

Deoximation. The transformation is carried out in aqueous MeCN at reflux. Friedel-Crafts alkylations. Alkenes and ethers are used as electrophiles in the reaction catalyzed by MofCO). Allyl acetates and alcohols are also suitable substrates. ... 

Phenols undergo Friedel-Crafts alkylations with allylic chlorides or allylic alcohols over solid acid catalysts such as acidic KIO clay. For example, 2-buten-l-ol gives 3-aryl-1-butene and 1-ary 1-2-butene, albeit in low yields (12%) (equation 11). Allyl carbocations are involved as the reaction intermediates in these reactions. ... 

We have further examined the reactions of thiolato-bridged diruthenium complexes with other unsaturated organic substrates. When the cationic Ru complex 4 is treated with cinnamyl alcohol in p-xylene, the allylated aromatic compound 18 is obtained in good yield (Equation 6). We assume a Tc-allyl intermediate because the reaction using l-phenylprop-2-en-l-ol gives, instead of cinnamyl alcohol, the same product 18 however, the detailed reaction mechanism is still obscure. This novel allylation reaction is halogen-free, and may replace the conventional Friedel-Crafts alkylation. 

Other reactions include enamination, " acetalization, dithioacetalization, Friedel-Crafts alkylation with allylic alcohols and tertiary alcohols."... 

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