A three-step mechanism involving the formation an
d rearrangement of an interme
diate with in
doline-azeti
dine spirocyclic core structure wasshown by DFT computations to account for the electrophilic cyclization of tryptophan
derivatives to hexahy
dropyrrolo[2,3-
b]in
doles. Thecorrespon
ding 3a-bromo
derivatives have been obtaine
d in high yiel
ds an
d synthetically useful
exo/
endo ratios.