Directed Fischer Indolization as an Approach to the Total Syntheses of (+)-Aspidospermidine and (-)-Tabersonine.

A conceptually new synthetic approach that provides general access to the aspidosperma alkaloids (+)-aspidospermidine and (-)-tabersonine was developed. This method is based on the regioselective indolization of an ene-hydrazide, which was obtained via a base-catalyzed intramolecular aza-Michael reaction, in situ trapping of the resulting enolate, and subsequent C-N coupling with phenyl hydrazide.

Visible-Light-Induced Synthesis of Carbazoles by in Situ Formation of Photosensitizing Intermediate.

A visible-light-induced synthesis of N-H carbazoles from easily accessible 2,2'-diaminobiaryls in the absence of any external photosensitizer is reported. The process only requires tBuONO and natural resources, visible light, and molecular oxygen for the synthesis of N-H carbazoles. Experimental and computational studies support that the in situ formation of a visible-light-absorbing photosensitizing intermediate, benzocinnoline N-imide, is responsible for the activation of triplet molecular oxygen to singlet oxygen that, in turn, promotes the synthesis of carbazole.