Reaction Elaboration

The different synthetic applications of acceptor-substituted carbene complexes will be discussed in the following sections. The reactions have been ordered according to their mechanism. Because electrophilic carbene complexes can undergo several different types of reaction, elaborate substrates might be transformed with little chemoselectivity. For instance, the phenylalanine-derived diazoamide shown in Figure 4.5 undergoes simultaneous intramolecular C-H insertion into both benzylic positions, intramolecular cyclopropanation of one phenyl group, and hydride abstraction when treated with rhodium(II) acetate. 

For a given adsorption constant, the observed electrochemical reversibility depends on the kinetic parameter defined as (O = Xy, or (o =. This reveals that the inherent properties of reaction (2.208) are very close to surface electrode reactions elaborated in Sect. 2.5. The quasireversible maximum is strongly pronounced, being represented by a sharp parabolic dependence of vs. m. The important feature of the maximum is its sensitivity to the adsorption constant, defined by the following equation ... 

Self condensation reactions. Elaboration of a skeleton in synthesi s. 

The split-and-pool synthesis not only simplifies the complexity of the combinatorial synthetic process, but also offers additional important benefits. To undertake a full range of solid-phase chemical reactions, elaborate reaction conditions are needed for some chemical transformations. These include, but are not limited to, low temperature and inert atmosphere conditions. Parallel synthesis of a thousand compounds requires handling of a thousand reaction vessels. The timely addition of sensitive reagents (e.g., butyl lithium) at low temperature (—78°) under inert atmosphere during parallel synthesis is not a trivial task. It can be done if sophisticated automated synthesizer equipment is designed to handle and tolerate such reaction conditions. Such a synthesis can alternatively be performed easily in a manual fashion using a split-and-pool method that requires only a limited number of reaction vessels. Examples from Nicolaou s17 and Schrei-ber s18,19 laboratories have shown that the split-and-pool method is the methodology of choice for the synthesis of complex and diversity-oriented combinatorial libraries. 

Other examples of this sensitivity coefficient approach are given by Bemasconi on the deprotonation of phenylnitromethane and by Thibblin on elimination reactions. Elaboration of the method takes into account variations in the coefficients within and between reaction series. ... 

Having achieved success in the key Suzuki cross-coupling reaction, elaboration of the carbon framework was now required. Pleasingly, treatment of the coupled product 18 with methyllithium generated the corresponding methyl ketone 10 in good yield (Scheme 5). Displacement of the oxidized auxiliary present in amide 19 was also attempted. However, treatment of oxidized amide 19 with methyllithium resulted in the formation of significant quantities of the undesired double alkylation product 21. 

P. M. Hierl, Z. Herman and R. Wolfgang, Chemical accelerator studies of isotope effects on collision dynamics of ion-molecule reactions elaboration of a model for direct reactions, J. Chem. Phys. 53, 660-673 (1970). 

Danishefsky et al. have achieved a synthesis of a methyl peracetyl-oc-hikosaminide (216), an undecose degradation product of the anthelmintic hikizimycin, in which use is twice made of the siloxy-diene aldehyde Diels-Alder reaction. Thus, the reaction between the diene (211) and furfural with [EuCfod) ] catalysis leads to the pyrone (212) which, after elaboration to (213), is again condensed with (211), but this time with magnesium bromide catalysis, which causes addition of the remaining four carbon atoms of the undecose in a chelation-controlled and, notably, a topically exo reaction. Elaboration of (215) to the required protected hikosamine (216) then follows in a straightforward manner. 

In a solution containing vesicles one can distinguish, at least, five reaction sites (Scheme 2) (1) the inner compartment, (2) the internal interface, (3) the hydrophobic bilayer itself, (4) the external interface and (5) the aqueous phase [35]. We decided to probe each site with appropriate test reactions, elaborate theoretical and experimental approaches to describe reagent distribution and reactivity in vesicle-containing solutions. 

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