Reagent path

FIGURE 3.15 Protection of amino groups as urethanes by reaction with succinimido carbonates (path A).33-36 The mixed carbonate is a weaker electrophile than the chloroformate. The V-alkoxycarbonylamino-acid anion does not react with the reagent (path B) in the presence of the weak base hence no dimer is formed. R = triethyl or dicyclohexyl. 

Figure 2. Bimolecular displacement mechanism for substitution reactions of square planar complexes. ka is the rate constant for the solvent path and ky is the rate constant for the direct reagent path.

This requires that a plot of kobs against [Y] be linear with an intercept of kx for the reagent-independent path and a slope of k2 for the reagent path. Such a two-term rate law... 

A remaining critical mechanistic question deals with the mode of product formation from the ion pair formed upon H abstraction. At this point, the reaction can be consummated either by transfer of H- from B to the carbonyl carbon (path a, Scheme 30), or direct abstraction of H- from another R3SiH reagent (path b).248 In this latter scenario, the borane becomes a spectator in the reaction, and the true catalyst is the [R3Si]+ cation. To probe this question, we performed the experiment depicted in Scheme 31. In the case of path b, both pairs of isotopomers should be observed, while if path a is operative, only the unscrambled products should be present. In fact, the product mixture consistent with... 

A one-electron transfer from substrate to reagent (path A), which was suggested by several authors, is quite possible because of the highly oxidizing properties of the F—Xe—L molecule, especially when part A of the organic molecule is electron-rich. 

The mechanism of this reaction was proposed by Kumada et al. and also by other research groups [2,3,246]. A simplified illustration, which is generally accepted and can rationalize other side reactions involving isomerization of the alkyl group of Grignard reagent (path a) and reduction of substrates (path b), is shown in Scheme 4. 

For each state scanning of intrinsic reaction coordinate was made on MC-SCF(14,ll)/aug-cc-pVDZ level from saddle point to reagents and products. Strac-ture corresponding to reagents valley is remote complex named at the following discussion. As a result, geometries and wave fimctions of points at TS-reagents path were found. 

In the rhodium catalyst/disilane system, the versatile arylrhodium intermediate 98 [73] is generated via loss of sUyl isocyanide (Scheme 6.20). If this arylrhodium 98 is intercepted by an external reagent (path a) before it undergoes silylation (path b), formation of a new C-C bond via C-CN bond cleavage is expected to... 

Where Kj and K2 are first and second order rate constants corresponding to solvent path and reagent path. 

The path shown in the clockwise direction is a solvent-intervention path. The solvent path follows SN mechanism, as shown in the figure. The path shown in the anti-clockwise direction is a reagent path. 

Track-etched membranes are made by exposing thin films (mica, polycarbonate, etc) to fission fragments from a radiation source. The high energy particles chemically alter material in their path. The material is then dissolved by suitable reagents, leaving nearly cylindrical holes (19). 

From intermediate 12, the path to periplanone B (1) is short but interesting. Enolization of 12 with lithium bis(trimethylsilyl)amide at -78 °C, followed by sulfenylation using Trost s reagent,12 affords a 16 1 mixture of regioisomeric monosulfenylated ketones favoring intermediate 17. The regioselectivity displayed in this reaction is... 

Enantiomerically enriched l-(diisopropylaminocarbonyloxy)allyllithium derivatives (Section 1.3.3.3.1.2.) add to carbonyl compounds with syn-l,3-chirality transfer21, giving good evidence for a pericyclic transition state in the main reaction path (Section 1.3.3.1.). However, since the simple diastereoselectivity and the degree of chirality transfer are low, for synthetic purposes a metal exchange with titanium reagents or trialkyltin halides (Section D.1.3.3.3.8.2.3.) is recommended. 

The relative stabilities of the species involved appear to be responsible for the stereochemical outcomes. Relief of ring strain must play a role in determining the course of the reaction. An explanation for the different reaction paths on using different Grignard reagents must wait further experimentation. 

In this cycle, (+)-l-phenyl-2-propanol is converted to its ethyl ether by two routes, path ab giving the (—) ether, and path cd giving the (+) ether. Therefore, at least one of the four steps must be an inversion. It is extremely unlikely that there is inversion in step a, c, or d, since in all these steps the C—O bond is unbroken, and in none of them could the oxygen of the bond have come from the reagent. There is therefore a high probability that a, c, and d proceeded with retention, leaving b as the inversion. A number of other such cycles were carried out, always with nonconflicting results. ... 

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