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  • Iridium-Catalyzed, Intermolecular Hydroetherification of Unactivated Aliphatic Alkenes with Phenols


    Metal-catalyzed addition of an O–H bond to an alkene is a desirable process because it allows for rapid access to ethers from abundant starting materials without the formation of waste, without rearrangements, and with the possibility to control the stereoselectivity. We report the intermolecular, metal-catalyzed addition of phenols to unactivated \(\alpha\)-olefins. Mechanistic studies of this rare catalytic reaction revealed a dynamic mixture of resting states that undergo O–H bond oxidative addition and subsequent olefin insertion to form ether products.


    Metal-catalyzed catalyzed hydrofunctionalization of alkenes offers the potential to control the regioselectivity, diastereoselectivity, and enantioselectivity of the addition process and to form products from readily accessible starting materials without the formation of waste. Metal-catalyzed hydrofunctionalizations also could be more tolerant of auxiliary functionality than acidcatalyzed additions and could occur without the rearrangements that are characteristic of acid-catalyzed additions to alkenes. Hydroamination (the addition of a N−H bond across an unsaturated C−C bond) remains one of the most studied transformations in hydrofunctionalization chemistry,(Müller 2008) but hydroetherification (the addition of an O−H bond across an unsaturated C−C bond) is much less developed. The ether products of hydroetherification are more often formed by substitution reactions than addition reactions.2 The electrophiles in substitution reactions are typically prepared by a multistep sequence that includes oxidation or reduction and functional group interconversion or activation of an alcohol. Moreover, these substitution reactions generate salt byproducts. Alternatively, ethers are formed by acid-catalyzed additions of alcohols to alkenes.3 However, the additions often require strong acids and high temperatures, form side products from isomerization of carbocationic intermediates, and occur without control of the product stereochemistry. Moreover, acid-catalyzed additions of phenols to alkenes occur with competitive reaction of the alkene at the O−H bond and at an ortho or para C−H bond.4 Metal-catalyzed hydroetherification would exploit the abundance and stability of alkene starting materials and could overcome many of the limitations of the classical syntheses of ethers. However, current hydroetherification reactions are limited in scope. Most reported metal-catalyzed hydroetherifications of unsaturated C−C bonds are intramolecular and occur with C−C multiple bonds that are more reactive than those of unactivated alkenes.5 Cationic gold complexes catalyze the cyclization of allenyl alcohols in high yield with excellent ee, but the reactions do not occur intermolecularly or with monoenes.6 Likewise, Ir, Pd, Pt, and lanthanide complexes catalyze intramolecular additions of alcohols to alkenes and alkynes, but intermolecular additions to alkenes catalyzed by such complexes are unknown.(Qian 2004)(Li 2005) Intermolecular hydroetherification of allenes with both carboxylic acids and phenols to form allylic ethers has been reported to occur in high yield and ee in the presence of a Rh catalyst, but the reactions do not occur with monoenes.(Kim 2008) Finally, intermolecular additions of alcohols to unstrained, isolated alkenes have been reported to occur in the presence of triflates of coinage metals.9 In these cases, the reactions form side products that are characteristic of carbocation intermediates.10


    This is task 6 to add reference here is one (Smith 2006) and here is another one (Hamilton 2007).

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