Chemoselectivity, definition

The form of the Hammond postulate just presented is very important in the analysis of the selectivity of many of the reactions we will discuss in this book in connection with chemoselectivity (definition in Section 1.7.2 also see Section 3.2.2), stereoselectivity (definition in Section 3.2.2), diastereoselectivity (definition in Section 3.2.2), enantiose-lectivity (definition in Section 3.2.2), and regioselectivity (definition in Section 1.7.2). 

Chemoselectivity is generally defined as the preferential outcome of one instance of a generalized reaction over a set of other possible reactions. In the context of this review, we will narrow this definition to a competition between homodimerizations and crossadditions of starting materials. 

Little has so far been reported on the chemistry of teUurones. The preparation of several dialkyl tellurones by H2O2 or air oxidation of the corresponding tellurides or telluroxides has been claimed, but it is doubtful whether those compounds were isolated in a pure tellurone form. In 1982 the first definitely characterized tellurone, bis(4-methoxyphenyl) tellurone (60), was prepared by periodate oxidation of the corresponding telluroxide (59 equation 50). Both (59) and (60) woric as mild useful oxidants which show some chemoselectivities and readily oxidize thiols to disulfides. The preparation of dodecyl 4-methoxyphenyl tellurone by a similar method has also been claimed. ... 

Extensive synthetic efforts have been made into the preparation of highly complex nucleosidic building blocks, whereby functionalization and conformational restriction were introduced via multiple ring incorporation into the glycosidic framework of the nucleotides. The introduction of such complexity has come at a price as these compounds often require lengthy synthetic sequences to achieve both chemoselectivity and stereochemical definition. 

Molecules such as proteins, sugars, and DNA are constructed by Nature in complex environments via simultaneous and/or cascade reactions. This chemoselectivity is today recognized by chemists as the Holy Grail for synthesis towards traly monodisperse macromolecules. The foundation of such accomplishments is based on an initial definition of orthogonal systems, established in 1977 by Barany and Merrifield, who noted that ... 

In Sect. 2.1 a chemoselective unicyclic mechanism was presented for a simultaneous hydroformylation and hydrogenation of cyclopentene. This mechanism, by definition, possesses intermediates of rally mraionuclear intermediates. The updated figure which provides emphasis to constraints is shown in Fig. 13 where additional... 

Selectivity is an important concept in chemistry [26]. It can be defined as the preferential outcome of a chemical process over a set of other plausible outcomes. A typical example is the case of enantioselectivity, where two enantiomers are in principle possible, but one of them is preferentially obtained. Enantioselectivity is one of the most interesting and most extreme cases of selectivity, as enantiomeric products have by definition the same energy. But the concept of selectivity is more general. Regioselectivity refers to the preference of one direction or chemical bond making or breaking above other alternative directions. Chemoselectivity refers to the reactivity of a chemical functional group in the presence of others. 

Professor Barry M. Trost has provided useful definitions of various kinds of selectivity that apply to nearly all chemical transformations (136). The ideal reaction is perfectly chemoselective ( performs a wanted stractural change and none other ), regioselective ( orients the reacting partners in correct fashion ), diastereoselective ( creates the correct orientations of the various parts of the molecule with respect to each other ), and enantioselective ( enables the formation of a molecule of one-handedness or a mirror image isomer ). None yet meets all of these goals. Considerable challenges and opportunities remain for practitioners of synthesis. 

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