SYNTHESIS OF 1-(PENTAFLUOROPHENYL)-BETA-CARBOLINE

Thermal condensation of tryptamine with pentafluorobenzaldehyde in ethanol afforded 1-(pentafluorophenyl)-1,2,3,4-tetrahydro-β-carboline (I, 51% yield), together with two by-products (IIa, 9% yield and IIb, 14% yield) which were produced by nucleophilic substitution of an aromatic fluorine atom by the tryptamine amino group. In solvent acetic acid, the same reactants gave 2-acetyl-1-(pentafluorophenyl)-1,2,3,4-tetra-hydro-β-carboline (III, 64% yield) as the main product, together with a reduced yield (20%) of I. Dehydrogenation of I with selenium dioxide provided 1-(pentafluorophenyl)-β- carboline (IV) in 84% yield; III also gave IV in 72% yield. Partial dehydrogenation of I with potassium permanganate provided 1-(pentafluorophenyl)-3,4-dihydro-β-carboline (V, 80% yield) but V could not be obtained from III. Indole itself provided (pentafluorophenyl)bis(3-indolyl)methane (VI, 82% yield) by simple reflux with pentafluorobenzaldehyde in propanol. In solvent acetic acid, the yield of VI was 78%. © 1990.