CYCLIZATION OF TRYPTOPHANS .3. THE CRYSTAL-STRUCTURE OF A PRODUCT DERIVED FROM TRIFLUOROACETYLATION OF NB-METHOXYCARBONYL-L-TRYPTOPHAN METHYL-ESTER IN PYRIDINE

The reaction between N(b)-methoxycarbonyl-L-tryptophan methyl ester and trifluoroacetic acid anhydride in pyridine furnished, as the main product, (2S,3aR,8aS)-dimethyl 3a-(N-trifluoroacetyl-1,4-dihydro-4-pyridyl)-8-trifluoroacetyl-1,2,3,3a,8, 8a-hexahydropyrrolo[2,3-b]indole-1,2-dicarboxylate. A second five-membered heterocyclic ring was formed through attack of the N(b) nitrogen to the 2-position of the indole ring system. Short intramolecular distances between the non-bonded electronegative atoms (O and F) and between fluorine and a benzene ring, are attributed to tight packing of the molecules in the crystal structure.