C-O coupling reactions

Vinylfurans can be formed from 2,3-epoxy-6-octenols via a C-O coupling reaction leading sometimes also to bicyclic ethers as by-product 1[67]... 

Scheme 5. New gold-catalyzed C-C and C-O coupling reactions TBDMS = tert-butyldimethylsilyl.

Interestingly, a first successful extension of the amination to oxygen nucleophils has been reported very recently. [19] Still at the beginning, this discovery opens the door to C-O coupling reactions for the synthesis of arylethers, including oxygen heterocycles. 

TPO is highly efficient in the two-electron oxidation of iodide to iodonium, which quickly reacts with the tyrosine residues of the Tg protein. The presence of iodo substituents on halogenated tyrosines favors the C—O coupling reaction when oxidized by Cpd I of TPO. 

The reaction sequence includes (1) an oxidative addition of C-X bond of the aromatic substrate Ar-X to a Pd° center, (2) a substitution of OR for X in the LnPd (Ar)X intermediate, and (3) a reductive elimination of the C-O bond from the Pd center. The ability of palladium(ll) alkoxides bearing p-hydrogen atoms to undergo p-hydride elimination imposes some limitations on the type of alkoxide groups that can be involved in these C-O coupling reactions [2]. The C(sp )-0 reductive elimination reactions from Pd and Pt centers have also been studied computationally [4]. The reactions were suggested to proceed via a concerted three-center mechanism. 

The mechanism of this polymerization reaction has been investigated thoroughly [15, 16]. However, even after more than 50 years since its commercial development, the mechanism of PPO formation is not fully unraveled [17,18]. In fact, the nature of the initial active species is still a matter of debate. Indeed, while some researchers consider that the C-O coupling reaction occurs via phenoxyl radicals (Figure 7.2b) [21], others believe that phenoxonium cations are involved in the polymerization process (Figure 7.2a) [22]. 

MeMgBr gave the tertiary alcohol 158, which upon a Buchwald-Hartwig C—O coupling reaction with stoichiometric Pd(OAc)2 provided murrayazoline (159). 

A novel Cu(OTf)2-catalyzed efficient synthesis of 2-arylbenzoxazoles through intramolecular oxidative C-O coupling reaction was developed by Ueda and... 

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