Dichlorodicyanoquinone Oxidations in the Indole Area. Synthesis of Crenatine

Article abstract of DOI:10.1021/jo00146a021

The influence of temperature on the reaction of dichlorodicyanoquinone (DDQ) with 1,2,3,4-tetrahydro-β-carbolines has been explored.The DDQ oxidation of amide 2a, when performed at room temperature, gave 3a (3-acylindole)/4 (2-acylindole) in a ratio of ca. 1:1, while this was increased to 2:1 at 0 deg C and to ca. 5:1 at -78 deg C.This method for preparation of 4-oxo-β-carbolines has been employed for synthesis of the β-carboline alkaloid crenatine (11).In addition, treatment of the 4-oxotetrahydro-β-carboline (3b) with hydrazine gave 1-ethyl-4-amino-β-carboline (12) which should provide access to a series of 4-substituted β-carbolines.