Specific transformation

The specific transformations that disconnect the strategic bonds in the desired fashion are performed. 

Select reaction conditions that would allow you to carry out each of the following stereo specific transformations... 

There are two principal biotechnological appHcations dealing with steroids. Microbial agents are used for processing raw materials into useful intermediates for general steroid production and for specific transformations of steroids to advanced intermediates or finished products (120,145). 

Homogeneous catalysis by transition metal clusters has been reviewed from the perspective of the specific transformations.Examples of very mixed-metal clusters catalyzing processes homogeneously are collected in Table IX. As is generally the case with homogeneous catalysis, the catalytic precursor is well defined, but the nature of the active catalyst is unclear. 

The most common chiral auxiliaries are diphosphines (biphep, binap and analogues, DuPhos, ferrocenyl-based ligands, etc.) and cinchona and tartaric acid-derived compounds. It is clear that the optimal chiral auxiliary is determined not only by the chiral backbone (type or family) but also by the substituents of the coordinating groups. Therefore, modular ligands with substituents that can easily be varied and tuned to the needs of a specific transformation have an inherent advantage (principle of modularity). 

Two further, more specific transformations leading to this ring system are shown in Scheme 56. 

Although this review is by no means comprehensive, it should give an impression of the great number of feasible syntheses of acceptor-substituted allenes and their possibilities of reactions. The unique combination of the C=C=C unit and the acceptor group often allows not only the common reactions of these parts but also specific transformations into a variety of very different products. Much attention was paid to the results of the last 20 years, but we have tried to mention all important facts about the chemistry of the title compounds. At the latest during the last two decades, it turned out that acceptor-substituted allenes are not only compounds for experts in organic chemistry but also very useful and general tools in synthetic chemistry. 

With this dialog box you can both check what restrictions have been established for a specific transform and read the comments introduced. Additionally, in the lower part, there is information on whether or not it forms part of a sequence of disconnections. In this particular case it reads "Unlinked," which shows that it is an individual disconnection, not forming part of a sequence. Further on there is an exercise on sequences of disconnection. Click "OK". 

As previously shown , transition-metal stabilized carbenes cannot be used as sources of free carbenes, due to their chemical inertness. However, selected reagents can operate specific transformations on these complexes (Scheme 11) ... 

In the interim period, results have accumulated steadily, in endeavors to address and extend the chemistry beyond the initial perceived limitations. These limitations include the following (a) the effective catalytic syntheses are confined to the reactions utilizing catecholborane (b) the scope of alkenes for which efficient rate, regio- and enantio-selectivity can be achieved is limited, and (c) the standard transformation mandates the oxidation of the initially formed (secondary) boronate ester to a secondary alcohol, albeit with complete retention of configuration [8]. Nonetheless, for noncatalytic hydroboration reactions that lead to the formation of a trialkylborane, a wide range of stereo-specific transformations may be carried out directly from the initial product, and thereby facilitate direct C-N and C-C bond formation [9]. 

A comparable paradigm of success is still to be established for more complex catalytic materials e.g., finite metal/compound clusters, mixed oxides, zeolites), many of which are highly important technological catalysts and often contain multiple active centers that are required to achieve a series of specific transformations. The local structures of these catalysts and... 

The range of species produced reflects the overall mechanistic scheme shown in Figure 1. The detail however gives insights into the different processes and the effectiveness of the catalyst components in catalysing a specific transformation. 

Chiral templates can be considered a subclass of chiral auxiliaries. Unlike auxiliaries that have the potential for recycle, the stereogenic center of a template is destroyed during its removal. Although this usually results in the formation of simple by-products that are simple to remove, the cost of the template s stereogenic center is transferred to the product molecule. Under certain circumstances, chiral templates can provide a cost-effective route to a chiral compound (Chapter 25). Usually, the development of a template is the first step in understanding a specific transformation and the knowledge gained is used to develop an auxiliary or catalyst system. 

Chemistry within a unimolecular micelle precursor boron superclusters by site- and depth-specific transformations of dendrimers. [G. R. Newkome, C. N. Moorefield, J.M. Keith, G. R. Baker, G. H. Escamilla, Angew. Chem., Int. Ed. Engl. 1994, 33(6), 666-668] [ 149]. 

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