UBC Theses and Dissertations
Novel chromium carbonyl complexes of dihydropyridines and their application to the synthesis of dehydrosecodine Ridaura-Sanz, Vincente Ernesto
The work presented in this thesis is aimed at the total synthesis of 14,21-dehydrosecodine (1). This substance is an indole derivative with reactive substituents at position 2 (an acrylic ester segment) and 3 (a 1,6-dihydropyridine system). The stabilization of the latter involved the generation of chromium carbonyl complexes employing trisacetonitriletricarbonylchromium (0) as the reagent with appropriate synthetic indole derivatives. In order to develop the required methodology for the preparation of the above complexes, the initial experiments employed simple dihydropyridine systems. Thus, when N-methyl-3-ethyl pyridinium iodide (4_1) was treated with NaBH^ in a two-phase system (ether - water), N-methyl-3-ethyl-1,2-dihydropyridine (46_) was obtained. When this compound was treated with the above complexing agent a mixture (ratio 1:2) of (N-methyl-3-ethyl-l,2-dihydropyridine) tricarbonylchromium (0) (4_3) and (N-methyl-3-ethyl-l, 6-dihydropyridine) tricarbonylchromium (0) (4_4) was obtained. Thermal isomerization of this mixture in refluxing cyclo-hexane afforded a 1 : 1 ratio of (4_3) and (4_4) . Liberation of the organic ligand could be achieved by stirring (43) and/or (4_4) with pyridine. The above strategy was applied to the indole intermediate, N-(2-carbomethoxymethyltryptophyl)-3-ethylpyridinium per-chlorate (_36) but only a low yield (2%) of the desired chromium complexes was obtained. These results prompted a change in the original synthetic strategy and a new approach was initiated by other coworkers in this laboratory. Some studies with the novel system (4_6) were conducted as they relate to position of alkylation. It was shown that (46) undergoes reaction with benzyl bromide to afford the 5-substituted derivative.
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