Reactions of indole derivatives with oxiranes and aziridines on silica. Synthesis of beta-carbolin-1-one mimic of pancratistatin.

[reaction: see text] Indole and several indoles functionalized at C-2 were condensed with oxiranes, vinyloxiranes, aziridines, and vinylaziridines in the solid state on the surface of silica. The yields of these reactions were compared to those obtained from Lewis acid-catalyzed ring-opening reactions performed in solution and found to be superior in each case. The solid-phase aziridine opening constituted a key step in the synthesis of the beta-carbolin-1-one mimic of pancratistatin. Methyl 2-indolecarboxylate was found to react on the silica gel surface with N-tosylvinylaziridine in 68% yield. A nine-step synthesis of the pancratistatin mimic has been attained. The additional key transformation in this synthesis involved silica gel-catalyzed opening of an epoxide and hydrolysis of an acetonide. Detailed experimental procedures and full characterization are reported for all new compounds.