Schemes citing

If the oxidation scheme cited above corresponds to the mechanism of the oxidation of polypropylene, then the dependence of the rate of absorption of oxygen on the hydroperoxide concentration should be depicted... 

If a sulfide RjS, capable of decomposing hydroperoxide without the formation of active products [72], is introduced into the polymer, then the following equation is added to the scheme cited above ... 

The scheme cited shows that during oxidation not only are gaseous products liberated, but also, at the same time, the structure of the polymer chain is substantially changed aldehyde and hydrojgrl groups ac-... 

The scheme cited includes reactions characterizing the basic directions of the process. 

Negatively coordinated groups are given before neutral coordinated groups in the examples of Werner scheme names above. Ewens and Bassett presented good reasons why that order should be reversed. The lUPAC rules (20) recommend that ligands be cited in alphabetical order regardless of their... 

Some reactions of penicillanoyl diazomethane derivatives are summarized in Scheme 22 (71JCS(C)3864, 80TL2451 and refs, cited therein). 

Coxon and Stoddart have directed their attention to the formation of penta-erythritol-derived cryptands. With these molecules, the strategy was to block one pair of hydroxyl groups as an acetal and form a crown from the remaining diol. In the first of the two reports cited above, this was accomplished by treating the 0-benzylidine derivative of pentaerythritol with base and diethylene glycol ditosylate. The crown was then treated with a mixture of UAIH4 and BF3 which gives partial reduction of the acetal as shown in (8.9), above. The monoprotected diol could now be treated in a fashion similar to that previously described and the benzyloxy cryptand (77) would result. The scheme is illustrated below as Eq. (8.10). 

Another route presented in the work cited above also finally furnished 16 and 17, although in this case, the intermediate 62, prepared in three steps from indigo (63) via the 0-acetates 64 and 65, served as the precursor leading to the key compound 61 (Scheme 10) [97H(45)1647]. Details of the synthesis of 64 had been given previously by Bergman (82CS193). 

Before discussing Beckwith s data on that basis, a brief mention must be made of investigations by Lown s group (Naghipur et al., 1989, 1990, and other papers cited there) who claim to have observed the formation of benzoxathiete (10.63) and its valence isomer monothio-l,2-benzoquinone (10.64) in the aprotic diazotization of 2-[(2,-acetoxyethyl)sulfinyl]aniline (10.62). Scheme 10-82 is an abbreviated form of the mechanism proposed by the authors. A more detailed experimental study is clearly required. 

Consider also the schemes in Problem 5.2. Their circuit analogs are shown here, and further examples are provided in the references cited in this section. 

One of the first published microwave-assisted synthesis of benzothiazoles is the condensation of a dinucleophile such as 2-aminothiophenol, with an ortho-ester (neat) in the presence of KSF clay in a mono-mode microwave reactor operating at 60 W under a nitrogene atmosphere [ 12] (Scheme 12). Traditional heating (oil bath, toluene as solvent and KSF clay) gave the expected products in similar yields compared to the microwave experiments but more than 12 h were required for completion. Solvent-free microwave-assisted syntheses of benzothiazoles was also described by attack of the dinucleophiles cited above on benzaldehydes and benzaldoximines [13] (Scheme 12). This methodology was performed in a dedicated monomode microwave reactor... 

The presence of redox catalysts in the electrode coatings is not essential in the c s cited alx)ve because the entrapped redox species are of sufficient quantity to provide redox conductivity. However, the presence of an additional redox catalyst may be useful to support redox conductivity or when specific chemical redox catalysis is used. An excellent example of the latter is an analytical electrode for the low level detection of alkylating agents using a vitamin 8,2 epoxy polymer on basal plane pyrolytic graphite The preconcentration step involves irreversible oxidative addition of R-X to the Co complex (see Scheme 8, Sect. 4.4). The detection by reductive voltammetry, in a two electron step, releases R that can be protonated in the medium. Simultaneously the original Co complex is restored and the electrode can be re-used. Reproducible relations between preconcentration times as well as R-X concentrations in the test solutions and voltammetric peak currents were established. The detection limit for methyl iodide is in the submicromolar range. 

As is outlined for ene reactions of singlet oxygen in Scheme 15, the prototypical ene reaction starts with the electron delocalization from the HOMO of propene to the LUMO of X=Y. The delocalization from the HOMO, a combined n and orbital with larger amplitude on n, leads to a bond formation between the C=C and X=Y bonds. Concurrent elongation of the bond enables a six-membered ring transition stracture, where partial electron density is back-donated from the LUMO of X=Y having accepted the density, to an unoccupied orbital of propene localized on the bond. As a result, the partial electron density is promoted (pseudoex-cited) from the HOMO (it) to an unoccupied orbital (ct n ) of alkenes. This is a reaction in the pseudoexcitation band. 

As predicted from the comparative rates for C=C over C=C hydrozirconation cited earlier, a (poly)enyne is selectively hydrozirconated at the alkyne moiety, whatever the position of the alkene function [138, 210] in the molecule. It can be exempUfied by the chemoselective hydrozirconation of 1,3-butenyne. One exception to this chemoselectivity has been reported, which showed the terminal alkene to react with 1 but leaving the TMS-substituted alkyne function intact (Scheme 8-25). 

Scheme 11.11 gives some representative preparative reactions based on these methods. Entry 1 is an example of the classical procedure. Entry 2 uses crown-ether catalysis. These reactions were conducted in the aromatic reactant as the solvent. In the study cited for Entry 2, it was found that substituted aromatic reactants such as toluene, anisole, and benzonitrile tended to give more ortho substitution product than expected on a statistical basis.180 The nature of this directive effect does not seem to have been studied extensively. Entries 3 and 4 involve in situ decomposition of A-nitrosoamides. Entry 5 is a case of in situ nitrosation. 

There are three features of a linker that will determine which support is applicable to a synthetic scheme (1) the functionality of the molecule at the anchoring position required for attachment (2) cleavage conditions and (3) the resulting functionality at the anchoring position of the molecule after the cleavage. As a continuing review on resins and linkers, this discussion will focus on the work that has been developed from 1997 to 1999 (Refs. 6-9 and references cited therein) and is described according to... 

Based on analogies we have cited, the kinetic scheme proposed for heavy-atom fluorescence quenching is reasonable and would predict the following relationship for fluorescence quenching ... 

Whereas this mechanistic proposal seems reasonable and no reason can be seen why it should not be cited to explain the allylic C/H insertion product from cyclohexene, other cases exist where cyclohexene is not the best substrate to distinguish between this and one of the other alternatives of Scheme 22. 

Only the general pattern of these reactions is described. In many cases the actual course of a reaction has not been elucidated, but for our purposes, the general schemes which are presented offer the opportunity to consider synthetic applications from a unified point of view. The schemes are broad in nature and possibly include some reactions still to be found. Examples illustrating the schemes do not cover the entire subject. They have been selected to provide evidence for the extensive nature of the field, particularly in the synthesis of natural products or of unusual molecules. Reactions leading to metal complexes and not to organic products have been excluded. Reactions occurring under mild conditions are naturally preferred. Reported yields, and the complexes employed, refer to the underlined references cited in the tables. 

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