Chloride anion capture

They proposed that [l,4]-sulfanyl participation gave a [2.2.1] bicyclic sulfonium salt intermediate 10a. This could be captured by the chloride anion to give either 19 (by path a) or 20 (by path b) as outlined in Scheme 3. It should be noted that the usual [l,2]-sulfanyl participation, via spirocyclic sulfonium ion 21, would only give the unrearranged chloride 19. 

The attempted trifluoromethylation of pentamethylcyclopentadienyllithium by reaction with F3 Cl in the presence of A-phenylmaleimide gave rise to the unexpected Diels-Alder adduct (25).37 The authors proposed that the cyclopentadienyl anion captures the iodine of CF3I to give (26) and trifhjoromethyllithium which then produces difluorocarbene (F2C ) which inserts into the C—I bond of (26) to form the difluoroiodomethylated product. The observed regioselectivity of addition of thiazyl chloride (N=S—Cl) to 2,5-diarylftirans provided support for a mechanism involving carbene and nitrene intermediates (27).38... 

An example is the capture of an electron by chlorine to give chloride anion. 

Carbamyl 1,2 and oxycarbonyl 5 chlorides have proven effective starter species although their cyclization-anion capture processes have been only briefly explored (Scheme 5.6.1)." The terminating species in Scheme 5.6.1 are alkynyl (1,5) and alkenyl (3) with pre-formed Sn(IV) capmre agents. These processes, as expected, are regio-and stereoselective and their full potential remains to be explored, but reference to Table 5.6.1 indicates the substantial leverage available from alternative terminating and anion capture species. 

In the third step, the carbocation intermediate is captured by a chloride ion, and the energy barrier for this cation-anion combination is relatively low. The transition state is characterized by partial bond formation between the nucleophile (chloride anion) and the electrophile (tert-butyl cation). 

Anwar, U., Fielding, M.R., Grigg, R.etal. (2006) Palladium catalysed tandem cychsation-anion capture processes. Part 8 [1] in situ and preformed organostannanes. Carbamyl chlorides and other starter species. J. Organomet. Chem., 691, 1476-87. 

Pentafluorophenoxy)ethyl-2-(piperidino)-ethanesulfonate (PFPES) as a new deriva-tization reagent has been used for the determination of cyanide in the presence of other anions using capillary gas chromatography-electron capture detector (CGC-ECD) [65]. The reactive cyanide and other anions such as iodide, nitrite, and thiocyanate in a liquid biphasic reaction system (PFPES does not react with fluoride and chloride anions) are derivatized. 

With a good source of external chloride anions the primary addition complexes 294 and 295 are captured in a p-attack to provide 296 and 297. 

A novel, three-component, palladium-catalyzed, cascade cyclization-anion-capture process which involves in situ generation of a zipper molecule has been reported. Thus, 2-iodobenzoyl chloride, an acetophenone imine, and carbon monoxide react in the presence of Pd(PPh3)2Cl2 to give isoindolin-l-one in moderate yield (eq 86). 

Sulfuric acid is normally used instead of hydrochloric acid in the diazotization step so as to minimize the competition with water for capture of the cationic intermediate Hydrogen sulfate anion (HS04 ) is less nucleophilic than chloride... 

Alkylation has also been used for the simultaneous determination of trace quantities of bromide and chloride by gas chromatography with electron - capture detection. The anions were derivatized with dimethyl sulphate. 

Acyliminium ions are also derived from rearrangement of Bischler-Napieralski cyclization products, which are obtained from amide product of reaction of arylethylamines and 2-methoxycarbonyl benzoyl chloride. These can be captured, for example, with methoxide anion (Scheme 43) (94TL(35)2751). 

Hydrolysis of Vinylogous Thioacetals. Carbanions prepared by lithiation of y-phenylthioallyl phenyl thioethers can serve as synthetic equivalents of /3-acyl vinyl anions. Umpolung of the usual electrophilic reactivity of 2-cyclohexenone is achieved by a sequence exploiting electrophilic capture of a hthiated vinylogous thioacetal and subsequent CuOTf-assisted hydrolysis (eq 57). Otherwise unfunctionalized vinylogous thioacetals can be hydrolyzed to enones by mercury(II) chloride in wet acetonitrile. However, the keto-substituted derivative in eq 57 gave only a 25% yield of enone by this method. A superior yield was obtained by CuOTf-assisted hydrolysis. ... 

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