Generation of Multi-Step Reactions

Poster Session Machine Generation of Multi-step Reactions in a Document from Single-step Input Reactions... 

POSTER SESSION MACHINE GENERATION OF MULTI-STEP REACTIONS IN A DOCUMENT FROM SINGLE-STEP INPUT REACTIONS... 

Chemical Abstracts Service (CAS) has created a protocol for machine generation of multi-step reactions within a document from the single-step reactions which are input. This protocol is being used in the CASREACT database for both explicit and imphed multi-step reactions. Both the input data and the output are described. Special features of this tool include ... 

Bob Dana and colleagues at Chemical Abstracts Service presented a poster on the machine generation of multi-step reactions for the CASREACT system on STN International. The online version of FIZ s Cheminform database will be available on STN International also. Alex Parlow gave a poster presentation on the creation of Cheminform both as an electronic database (for onhne and in-house use) and as a printed product. 

Blower Jr., P.E. Chapman, S.W. Dana, R.C. Erisman, H.J. Hartzler, D.E. Machine Generation of Multi-Step Reactions in a Document from Single Step Input Reactions . In Chemical Structures The International Language of Chemistry Warr, W.A., Ed., Springer-Verlag Heidelberg, 1988 pp. 399-407. 

As described above, carbamoylnitrile oxides have not been widely used for organic syntheses because of multi-step reactions of precursors or severe reaction conditions. In this chapter, another generation method for 6 from easily available nitroisoxazolone 10 [27] is introduced, which proceeds under mild conditions without using any special reagents. 

A chemical intermediate is a species that is neither starting material nor product and occurs only in multi-step reactions. The term chemical intermediate should not be mixed up with the term transition state. While the latter portrays the geometry of highest potential energy along the reaction coordinate of an elementary reaction step, the former describes an individual, albeit short-lived, chemical compound with transition states leading to and from it. When generated in a chemical reaction, intermediates will quickly con-... 

While the application of enzymes and proline as catalysts for the (commercial) formation of carbon-carbon bonds is relatively new, transition metal catalysts are well established for the industrial synthesis of carbon-carbon bonds. Although in themselves not always perfectly green, transition metal catalysts often allow the replacement of multi-step and stoichiometric reaction sequences with one single catalytic step. Thus, the overall amount of waste generated and energy used is reduced drastically [61-64]. 

In the primary reductive step, oxygen from air or Fe(III) ions function as electron acceptor. The radical cation l+ , generated in the oxidative counterpart, loses a proton, affording the strongly reducing a-amino radical (Figure 10), which injects an electron into the conduction band of CdS. Hydrolysis of the resulting iminium salt leads finally to the secondary amine. Repetition of this multi-step reaction affords the completely demethylated product 2. 

Many of the C-F activation reactions discussed in this account are complicated by multi-step reaction sequences and secondary reactions with solvent or fluoride ion generated in the course of the transformation. In catalytic systems, the additional reagents needed to achieve catalytic turnover may cause undesired side reactions to take place. Gas-phase ion molecule reactions provide one way to study model systems in the absence of these complicating factors to obtain fundamental information on the C-F activation process [84]. In addition, theoretical treatments of C-F bond activation are beginning to provide insight into these transformations. 

By computer simulation, mathematical models of both the color formation and the deactivation process, involving multi-step reaction sequences, could be established and correlated with actual experimental results. These models allowed computer generation of practical sensltometrlc curves (138,139). 

OS 57] [R 6] [P 40] One of the first examples of parallel multi-reaction was performed in a Caliper chip [18], By 2 x 2 combinations of two aldehydes and two 1,3-diketones, four cycloadducts were generated simultaneously in one run on one chip (Figure 4.71). The conversions were comparable to those for the single runs, with one exception. Also, cross-contamination was observed. It ranged from a few percents to about 50%. It should be pointed out that despite these initial drawbacks the demonstration of multi-reaction feasibility is a further valuable step in micro channel processing. 

Evidently Seyferth was the first to recognize the new opportunities of such variations in organosilicon chemistry.16 He generated dimethylsilylene in the presence of ketones and phosphines. According to authors hypothesis multi-step transformation takes place in the reaction (Scheme 2). 

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