Reagents, reactive intermediate generation

You have already had considerable experience with carbanionic compounds and their applications in synthetic organic chemistry The first was acetyhde ion m Chapter 9 followed m Chapter 14 by organometallic compounds—Grignard reagents for example—that act as sources of negatively polarized carbon In Chapter 18 you learned that enolate ions—reactive intermediates generated from aldehydes and ketones—are nucleophilic and that this property can be used to advantage as a method for carbon-carbon bond formation... 

Jayalekshmy and Mazur illustrated the reduced mobility of polymer-bound reagents by delayed trapping of reactive intermediates generated within a polymer matrix 139). 

Base-free uncomplexed silylene complexes are so far only known as reactive intermediates which are generated at low temperatures and trapped by suitable reagents. Several publications related to this subject are known, but most of the work is now summarized in review articles [95]. 

Whereas the original Moffat-Pfitzner oxidation employs dicyclohexylcarbodiimide to convert DMSO into the reactive intermediate DMSO species 1297, which oxidizes primary or secondary alcohols via 1298 and 1299 to the carbonyl compounds and dicyclohexylurea [78-80], subsequent versions of the Moffat-Pfitzner oxidation used other reagents such as S03/pyridine [80a, 83] or oxalyl chloride [81-83] to avoid the formation of dicyclohexylurea, which is often difficult to remove. The so-called Swern oxidation, a version of the Moffat-Pfitzner oxidation employing DMSO/oxalyl chloride at -60°C in CH2CI2 and generating Me2SCl2 1277 with formation of CO/CO2, has become a standard reaction in preparative organic chemistry (Scheme 8.31). 

Nitrile sulfides (37) have some, admittedly slight, structural affinity with the other nitrogen-sulfur reagents discussed in Section IV. They are unstable reactive intermediates that can be generated by the thermolysis of 1,3,4-oxathiazol-2-ones (38) or of 1,3,4-oxathiazoles (39).41 42 An alternative preparation is by the elimination of 2 moles of hydrogen fluoride from imini-sulfur difluorides (Scheme 5).43 Nitrile sulfides (37) are capable of undergoing... 

Taking advantage of the competition principle, Bottini et al. [54] determined relative rate constants (krei) for the interception of 6 by conjugated dienes and styrene. Three precursors of 6 were employed, 32b, 33a and 35 (see Scheme 6.9), and also the solvent and the temperature were varied. If the polymerization of styrene and the dimerization of 1,3-cyclopentadiene are taken into account, the various sets of krei values agree well with each other and indicate the same reactive intermediate 6 under all conditions tried. Obviously, 6 is uncomplexed rather than associated with a metal halide, formed on generation of 6, or magnesium, which is the reagent for the liberation of 6 from 33a. The kre values obtained from experiments with 35 are summarized in Scheme 6.19. 

If the experiment is conducted properly, this method has the advantage that the reactive intermediate to be studied is truly isolated in the sense that it is (ideally) surrounded by nothing but the inert host material (doped perhaps with some deliberately added reagent). This feature can be very important, say, in the case of radicals which usually arise in parrs that have a propensity to recombine if trapped in the same matrix cavity, which often excludes method (3) above for the generation of such species. 

POLYHYDROGEN FLUORIDE REAGENT 1-FLUORO-ADAMANTANE. Dichloroalkane synthesis is shown in cis-DI-CHLOROALKANES FROM EPOXIDES cis-1,2-DICHLORO-CYCLOHEXANE. Nitrile functionality can be introduced from a ketone, as in NITRILES FROM KETONES CYCLOHEXANENITRILE, or from a reactive diene, as shown in 2,3-DICYANOBUTADIENE AS A REACTIVE INTERMEDIATE BY in situ GENERATION FROM 1,2-DICYANO CYCLOBUTENE 2,3-DICYANO-1,4,4a,9a -TETRAHYDRO-FLUORENE. 

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