Dealkylation-realkylation

C H3MgI and reduction of the indol system afforded the anthelmintic drug substance 188 ([ H]PNU-141962, 2-desoxo[l -methyl- H3]paraherquamide), thereby reconstituting the skeleton of 184 in a slightly modified form. The synthesis depicted was designed as a pilot smdy for the preparation of the respective tritium and carbon-14-labeled isotopomers. It illustrates a more general C-dealkylation-realkylation approach that is otherwise difficult to accomplish (Section 10.1.2). ... 

The thiono-thiolo rearrangement I- -11 is catalyzed by II as well as by decomposition products of II Me2S induces an O-dealkylation/S-realkylation sequence (4), and Me3S acts as an alkylating agent superior... 

The thioalkyl-containing macrobicyclic complexes have been dealkylated and realkylated easily under the action of potassium thiolates in aprotonic media (Scheme 14). The products of de- and realkylation reactions were detected by PD and FAB mass spectrometry. In this respect the thioalkyl-containing clathrochelates are close to the aryl alkyl sulfides. In the course of thioalkyl derivative synthesis with an excess of potassium thiolate, a mixture of dealkylated products was obtained in addition to the desired hexathioalkyl clathrochelates. The addition of corresponding alkyl iodide and potassium carbonate to the reaction mixture in the final stage of reaction led to an increase in yields by alkylation of HS groups, resulting in the side dealkylation process [65]. 

The alkaloid delphonine (CCXVII) was also claimed to have been isolated from both the roots and aerial portions of Delphinium rotundi-folium Afan. (118). Although it was not compared with an authentic sample, the physical constants, character of the functional groups, and analytical data for the newly isolated alkaloid were close enough to those reported for delphonine that they were assumed to be identical. However, when the A-dealkylated derivative was realkylated with methyl iodide... 

Konig et al. [274] investigated the long-term stability of two selected ILs over several months under process-hke conditions with a subsequent IC-MS analysis to identify the resulting decomposition products. As an example, samples of the imidazohum-based ILs l-ethyl-3-methylimidazolium chloride (EMIM Cl) and 1-ethyl-3-methyhmidazohum acetate (EMIM Ac) were thermally and catalytically stressed. The most obvious decomposition of a dialk)dimidazolium cation is the reverse reaction of the quaternization reaction. The typical products are imidazole derivatives and alkylated anions (reaction (1) in Figure 8.120). Further considerable decomposition products are cations with scrambled alkyl chains. These cations can be formed either due to a realkylation of a previously dealkylated... 

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