Synthesis of optically pure pyrroloquinolones via Pictet–Spengler and Winterfeldt reactions

Diastereomers of substituted 2,3,4,9-tetrahydro-1H-β-carbolines were synthesized via asymmetric Pictet–Spengler reaction of the chiral tryptamine derived from R-1-naphthalen-1-yl-ethylamine with 67% of d.e. The S,R-β-carboline can be converted to the R,R form by treating with TFA. Optically pure pyrroloquinolones were obtained from Winterfeldt oxidation of the β-carbolines without epimerization.