A SIMPLE ENTRY INTO THE SERIES OF TETRACYCLIC HETEROYOHIMBANES 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 allowe d to react with trifluoroacetic acid for a few minutes. Similarily, 4b and 4c give by treatment with SnCl2 and heat in an [4+2]-cycloadditio n reaction the spiroindolines 17 and 18. Oxytryptamine reacts with 2 m oles of 2 to give immediately the spirooxindole 21. This compound can be rearranged to give 23 (after treatment with acid, reduction and cat alytic hydrogenation). 23 has the cis-configuration of rhyncophylline.