Cycloaddition von N-Phenylmaleinimid an (1,2,3,6-Tetrahydropyridyl)-indole

1-Methyl-2-and 1-methyl-3-(1-methyl-1,2,3,6-tetrahydro-4-pyridyl)-indole undergo 1,4-cycloaddition (formally of the DIELS -ALDER -type) with N-phenyl-maleimide, leading to the pentacyclic compounds III and IV.