External reagents synthesis

Greaney and coworkers have introduced the conjugate addition of thiols to Michael acceptors as an effective adaptive DCL strategy [46,47]. The reaction is well suited for biological DCL synthesis, taking place in water with no requirement for external reagents. As with disulfide bond formation, the reaction is subject to simple and effective pH control. Under mildly basic conditions, the thiolate anion adds rapidly to Michael acceptors under equilibrium conditions. Acidification effectively switches the reaction... 

The choice of substituents is of crucial importance for the successful synthesis and isolation of polyhedral silicon compounds. The Si—Si bonds of the small-ring compounds are readily oxidized because of the existence of high-lying orbitals and their inherent high strain. Therefore, the full protection of the skeleton by bulky substituents is required to suppress the attack by external reagents. 

Abstraction reactions are elimination reactions in which the coordination number of the metal does not change. In general, they involve removal of a substituent from a ligand, often by the action of an external reagent, such as a Lewis acid. Two types of abstractions, a and 3 abstractions, are illustrated in Figure 14-12 they involve, respectively, removal of substituents from the a and P positions (with respect to the metal) of coordinating ligands. a-Abstraction has been encountered previously, in the synthesis of carbyne complexes discussed in Section 13-6-3. 

Recently, Ireland et al. described a multistep synthesis of the trans-syn-trans diketone 53 from the readily available enedione (50) (Scheme 5). Direct saturation of the enone by either metal-ammonia or catalytic reduction had previously proven to yield only AB cw-fused material.The tendency for 3-foce attack is understandable from models, in which it appears that the a-C-8 methyl group shields the a-side of the C-5 carbon from approach by an external reagent. 

Project information describing hypotheses, where compounds are at in a project and decisions made with respect to templates and particular compounds Miscellaneous special purpose databases (e.g., ACD, GeneGo, ChEMBL, custom databases of hterature data built under contract, external chemistry synthesis tracking database, a high throughput reagent database)... 

It has now been demonstrated beyond any doubt that it is possible to use self-assembly processes to construct molecular assemblies and supramolecular arrays, which are of nanometre-scale, with a high degree of control and precision from molecular components comprised of simple and inexpensive building blocks. Furthermore, it is often easier to make molecular assemblies and supramolecular arrays than it is to make some of the components on their own. The molecular components are "intelligent in that they hold all of the information necessary for the construction of the precisely assembled structures and superstructures without the need for external reagent or catalysis. It is becoming increasingly obvious that self-assembly occurs under very precise constitutional and stereochemical control. The viability of self-assembly as a concept for the synthesis of novel molecular architectures on the nanometre-scale is surely vindicated by now. 

Along with the guidepost (Wegner, 1972, 1973) based on the crystal-to-crystal transition from 2,5-DSP to poly-2,5-DSP, absolute asymmetric synthesis has been achieved by the topochemical reaction of a chiral crystal of an achiral diolefin compound in the absence of any external chiral reagents. 

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