A simple and stereospecific synthesis of the triketolactam 15 is described. This compound has been previously converted to napelline 1. The key step of the synthesis is the rearrangement of the "denudatine" intermediate 11 to the napelline derivative 12. The denudatine skeleton was constructed by a stereospecific diene addition belween the o-quinone acetal 4 and benzyl vinyl ether. It is expected that this last process will be capable of general application in the synthesis of complex compounds.
. Can. J. Chem. 56, 1102 (1978). The construction of the C / D ring system of the alkaloids chasmanine and napelline by modification and rearrangement of a common intermediate is explored o n model compounds.The phenolic acid 9 was oxidized to the spirolactone 10. Addition of benzyl vinyl ether to this material gave the adduct 28 in high yield. This central 'nordenudatine' type intermediate was then modified (in a very few stereospecific steps) to the 'napelline' model compound 47 and to the keto acetal38. Con~pound 38 is an intermediate of our photochemical route and we have already described its conversion to a chasmanine model derivative.The new syntheses of chasmanine and napelline foreshadowed by the present niodel studies are expected to be completely stereo-and regiospecific, alniost 10 steps shorter and a n order of magnitude more efficient than the total syntheses of these two alkaloids which we have reported in the recent past.Incidentally, with these ~ilodel studies, the methoxy ketone 20 was prepared. The methoxyl in this compound is epinieric to the corresponding (C16) niethoxyl of the aconite alkaloids. Some relevant observations on the nmr spectra and allylic rearrangement (pyro-isopyro rearrangement) of this material are also reported. On etudie, sur des composts modeles, la possibilitt de construire les systtmes des cycles C/D des alcaloides chasmanine et napelline par une modification et une transposition d'un intermtdiaire commun.On a oxydt I'acide phenolique 9 en spirolactone 10. L'addition d'ether benzylvinylique ce compose conduit a I'adduit 28 avec un bon rendenlent. On a alors modifit cet intermediaire central de type "nordenudatine" (a I'aide de quelques etapes tres stertospCcifiques) pour conduire au conipose niodele 47 "napelline" et au ceto-acktal 38. Le conipose 38 est u n intermediaire dans notre voie photochimique et nous avons deja decrit sa transformation en un dtrivt modele de chasmanine.On prevoit que les nouvelles syntheses de la chasmanine et de la napelline preconistes par les presentes etudes modeles seront conipletement stereo-et regiospecifique, qu'elles comporteront dix etapes de nioins et seront au noi ins 10 fois plus efficaces que les syntheses totales de ces deux alcaloi'des qui ont ete rapportis recemment.Incidemment, avec ces etudes modeles, on a prepare la methoxy cetone 20. Le groupe nlethoxy de ce compose est en position epimtre par rapport au groupement methoxy correspondant (C16) des alcaloi'des de I'aconite. On rapporte aussi quelques observations appropriees concernant les spectres rlnn et la transposition allylique (transposition pyro-isopyro) de ce conipost.[Traduit par le journal] Introduction We have shown (1) that a route proceeding via denudatine-type intermediates is very advantageous for the construction of polysubstituted C19 aconite alkaloids and very recently we have successfully completed a stereospecific total synthesis of the alkaloid chasmanine I using such a route (2). In this synthesis the denudatine-type intermediate 11 was constructed by a...
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