Reaction of deprotonated α-(alkylidenamino)nitriles with
gramine in the presence of tributylphosphine furnishes α-substituted
imines of tryptophane nitrile. Their subsequent intramolecular cyclization
followed by dehydrocyanation and oxidation affords 1,3-disubstituted β-carbolines.
imines - α-aminonitriles - cyclization - alkaloids - β-carbolines