Nucleophilic trapping agents

Titanium tetrachloride promoted coupling of ethyl glyoxylate and dihydrofuran with subsequent reaction of the intermediate with a nucleophilic trapping agent provides a new route to functionalized tetrahydrofurans <99TL1083>. 

A very useful parameter that would tend to take the results a little out of the emotional realm would be a measure for electrophilic compounds, that is, total electrophilic compounds. That should be easy enough to do with these presumably direct-acting materials. There could be a standard method using nucleophilic trapping agents. 

Nucleophilic trapping agents used in the Type II Ac-Pd process are not limited to MeOH and other alcohols. A wide range of heteroatom and carbon nucleophiles may be used as in the cases of the Type II cyclic carbopalladation processes terminated by various nucleophilic reagents (Sect. 2.1.2). A couple of reactions shown in Scheme 58 [ 145] provide additional examples of heterocycles synthesis via Type II Ac-Pd process terminated by cross-coupling. 

Photolysis of sulphonyl azides in the presence of nucleophilic trapping agents such as dimethyl sulphoxide or dimethyl sulphide gave imine derivatives. For example, irradiation of -toluenesulphonyl azide in dimethyl sulphide gave a 54% yield of iV-( -toluenesulphonyl) dimethylsulphimine (375) The use of dimethyl sulphoxide resulted in lower yields of the trapped nitrene (377) (13-32%), and... 

This reaction can also be utilized when there are heteroatom substituents. Reaction of amide-diene 97 with paraformaldehyde and formic acid generated iminium salt 98. Cationic cyclization (formate is the nucleophilic trapping agent) generated the perhydroisoquinoline 99. A related cyclization procedure that involves... 

Reaction of iV-[(benzotriazol-l-yl)methyl]amide 707 with PCI5 gives chloroimine 708, which upon treatment with Bu OK is converted to nitrile ylide 709. Benzyl esters of ot,(3-unsaturated acids used as dipolarophiles trap species 709 to generate pyrroles 712 (Scheme 110) <2002JHC759>. When no trapping agent is added, the N-2 atom of benzotriazole act as a nucleophile, and tricyclic system 711 is formed <2001TL9109>. Addition of benzyl bromide... 

Although halosilanes undergo smooth nucleophilic substitution at the silicon, they are rather inert to redox reactions. Therefore, chlorosilanes are usually used as trapping agents of anionic intermediates generated by electroreduction of organic compounds. However, in the absence of other reactive substrates halosilanes are reduced electrochemically to form Si-Si bonds. Indeed, there are a number of reports in the literature of the cathodic reduction of chlorosilanes (Sect. 4.2). 

However, the fate of the intermediate carbanion can depend on the nucleophile, the presence of appropriate electrophiles as trapping agents and the solvent, e.g. Scheme 42 [96], Examples to illustrate these processes are drawn from more recent literature in Table 3. 

On the contrary, in the case of 1-iodonorbomane (a tertiary halide), the result of the reaction with trimethylstannyl reagents (Me3SnM, M = Li, Na), both in the absence and in the presence of trapping agents, confirmed that the nucleophilic substitution process is governed by competition between polar and radical mechanisms133. 

Historically it was the gas-phase process which first unequivocally proved the existence of species with a 7rbond to silicon [Eq. (37)] (198). In the absence of nucleophiles, the dimethylsilene gives a head-to-tail dimerization product, l,l,3,3-tetramethyl-l,3-disilacyclobutane. On the other hand, addition products across the double bond of the intermediate silene are formed in the presence of various trapping agents. 

Trapping agents, such as malonate anions, naphthoxides, and phosphines have been used to determine the concentration of chain carriers in controlled/living and other carbocationic systems [85,249,250]. These strong nucleophiles react with all sufficiently electrophilic species, including not only carbocations but also onium ions and covalent esters. Thus, the discussed measurements can provide only the total concentration of active and dormant end groups. In principle, the kinetics of formation of the product in the trapping experiments could resolve more and less active species but only if they are present at comparable concentrations. As discussed before, carbocations are present in ppm quantities in comparison with dormant species. 

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