| Abstract: | The pyrrolo-indoles 9, 10 and 12 have been isolated as by-products. The structure of carbinolamine 13, a potential precurser of pyrrolo 2,3-f] indoles, was examined by chemical and spectroscopic methods. Under Nenitzescu-conditions 13 could not be reduced to the pyrroloindole 11, but the furano-indolenin 16 was isolated. The origin of the pyrrolo 3,2-e] indole 12 from carbinolamin 17 was proved by a corresponding reaction. The course of the reaction via the ring-opening of the indole 19 can be excluded and thus a direct ring-closure of F is made probable. Attempts to reduct 17 show that the carbinolamine can not be considered as a precursor of hydroxyindoles in an apolar, aprotic medium. Thus a reaction corresponding to an oxidation-reduction mechanism is not possible under these conditions. The experiments indicate that another mechanism, namely the direct cyclisation of H in this case leads to indole formation. |
