Rapid Access to the Welwitindolinone Alkaloid Skeleton by Cyclization of Indolecarboxaldehyde Substituted Cyclohexanones

[reaction: see text] A very rapid access to cyclohexanone-bridged indole systems was established by an acid-mediated ring closure of appropriately substituted indole aldehydes, which involved an apparent disproportionation of an aldol-like intermediate. One of the bridged indole intermediates was further transformed into an oxindole having the essential skeleton of the Welwitindolinone alkaloids.