C-O bond-forming

The most widely accepted mechanism of reaction is shown in the catalytic cycle (Scheme 1.4.3). The overall reaction can be broken down into three elementary steps the oxidation step (Step A), the first C-O bond forming step (Step B), and the second C-O bond forming step (Step C). Step A is the rate-determining step kinetic studies show that the reaction is first order in both catalyst and oxidant, and zero order in olefin. The rate of reaction is directly affected by choice of oxidant, catalyst loadings, and the presence of additives such as A -oxides. Under certain conditions, A -oxides have been shown to increase the rate of reaction by acting as phase transfer catalysts. ... 

Starting from n-butane, 2-butoxides that rapidly convert to 2-butanone are found over MgCr204 [24]. However, the further oxidation of adsorbed 2-butanone only gives rise to the acetate species, while starting from n-butane, formate species are also observed. This can be explained assuming that sec-butoxides can partly isomerize to rert-butoxides before further oxidation. This implies that the C-O bond formed is partly ionic and the alkyl moiety has the... 

Catalytic Asymmetric C-O Bond Forming Reactions in Total Synthesis... 

The first reaction occurs in a single bimolecular elementary step in which OH- displaces Br with the C-O bond forming as the C-Br bond is breaking. The (CH3)3C group is too bulky to allow close approach... 

Harada, T. Mukaiyama, T. Trityl antimonate-catalyzed sequential reactions of epoxides with silylated nucleophiles. Rearrangement of epoxides and C-C or C-O bond forming nucleophilic reaction onto the intermediate carbonyl compounds. Bull. Chem. Soc. Jpn. 1993, 66, 882-891. 

The arylation of aliphatic alcohols is particularly challenging because the competitive /1-hydride elimination side reaction that was problematic in the amine arylation is even more prevalent in the analogous C-O bond forming reactions. Thus, the coupling of tertiary alcohols such as ferf-butanol and aryl halides has seen considerable success, while general methods for the arylation of primary and secondary alcohols have been more elusive. 

I eroxyacids transfer an oxygen atom to the alkcne with syn stereochemistry—both C—O bonds form on the same face of the double bond— through a one-step meclranism without intermediates. The oxygen atom fartliest from the carbonyl group is the one transferred. 

Palladium-catalyzed C—N bond and C—O bond-forming reactions... 

Enolates are undoubtedly the most versatile intermediates for C-C, C-N, C-O bond-forming reactions [36]. Continuous progress has been made not only in fundamental operations involving these anionic species but also during the synthesis of complex natural products. Compared with metal enolates with counter cations of, e.g., B, Si, Li, Na, K, Mg, Ti, Sn, Cu, etc., aluminum enolates have found fewer apphcations, probably because no particular advantages over the other metals have been perceptible. There are, however, still intriguing aspects of novel reactivity and selectivity in the formation and reaction of aluminum enolates. Specifically, very recent development have highhghted pre-formation of Lewis acid-carbonyl complexes by use of bulky aluminum compounds as precursors of aluminum enolates the behavior of these complexes is unprecedented. 

Figure 3, Incorporation patterns from isotope-labeled acyl CoA precursors and proposed unified biosynthetic pathways for (A) nonactin (7) and (B) paramycin 607 (9, coupling between intermediates 14 and 15) and 593 (10, coupling between intermediates 14 and 16) featuring C-O bond-forming PKSs such as...

Scheme 5.40. Bismuth(III) salt-mediated C-O bond forming reactions.

A selective activation of the C—F bond by Yb(OTf)3 has been employed in an elegant C—O bond forming reaction for joining ring E and ring H fragments of Ciguatoxin (Scheme 3.41) [3]. The activation of the C—F bond in 8 by ytterbium triflate is much more effective than... 

We ll start with some epoxidation reactions. Of course these form rings, and you have seen, in Chapter 20, epoxidations of alkenes such as cyclohexene. We said in Chapter 20 that epoxidation was stereospecific because both new C-O bonds form to the same face of the alkene. 

Unlike H-atom transfer, C—O ring closures are highly exothermic processes because of stronger C—O bonds formed from cleavage of weaker 0—0 bonds, less the ring strain of the ether. For the simplest cases of epoxides or oxetanes, in which ring strain is 26—28 kcal mole-1 [13]... 

Dick AR, Kampf JW, Sanford MS (2005) Unusually stable palladium(IV) complexes detailed mechanistic investigation of C-O bond-forming reductive elimination. J Am Chem Soc 127 12790-12791... 

In the final step, the oxyanion must act as the nucleophile and the electrophile is benzyl bromide. The arrows start on the negative charge, and show the new C-O bond forming and the old C-Br bond breaking. 

Some fundamental inorganic chenustry that is important for understanding which complexes will undergo the aromatic C—and C—O bond-forming processes will be presented before the catalytic transformations. First, the three reaction types involved in the catalytic cycle to form arylanunes are similar to those found in the catalytic cycle for C—C bond formation oxidative addition of aryl halide to Pd(0) complexes, transmetallation that converts an arylpalladium halide complex to an arylpaUadium amido complex, and reductive elimination to form a C—or C—O bond. The oxidative addition step is identical to the addition that initiates C—C bond-fomting cross-couplings,f f but the steps that form the arylpalladium amido complexes and that produce the arylamine product are different. The mechanism for these steps is discussed after presentation of the scope of the amination process. 

Recent advances in manganese(lll) acetate-mediated organic synthesis, particularly that using free-radical C—C and C—O bond-forming reactions of various heterocycles 13RCA18716. 

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