Ein einfacher Zugang zu den tetracyclischen Vorläufern der Hetero‐ und Secoyohimbane, Strychnos‐ und Oxindolalkaloide

A Simple Entry into the Series of Tetracyclic Hetero‐ and Secoyohimbanes, Strychnos and Oxindole Alkaloids The divinylogous urethane 4a reacts in diluted acetic acid to give the indolochinolizine 9 (yield 40%). The total amount grows up to 65%, if compound 14 , prepared from 4a in nearly quantitative yield, is allowed to react with trifluoroacetic acid for a few minutes. Similarily, 4b and 4c give by treatment with SnCl 2 and heat in an [4+2]‐cycloaddition reaction the spiroindolines 17 and 18 . Oxytryptamine reacts with 2 moles of 2 to give immediately the spirooxindole 21 . This compound can be rearranged to give 23 (after treatment with acid, reduction and catalytic hydrogenation). 23 has the cis ‐configuration of rhyncophylline. magnified image