Reaction of Chiral Nucleophiles with Pyridinium Compounds. Total Synthesis of the Indole Alkaloids (−)-Isovallesiachotamine and (+)-Vallesiachotamine†

The addition of the chiral nucleophiles Na-2 and Li-5 to pyridinium compounds 1 and the subsequent ring closure (Pictet-Spengler cyclization) to indoloquinolizines 3a and 7b, respectively, proceed stereoselectively (d.e. for 3a: 54%; for 7b: ≥95%). Proof for the absolute configuration of these products is provided by their CD spectral data and the transformation of 7b into the indole alkaloids (+)-vallesiachotamine [(Z)-6] and (-)-isovallesiachotamine [(E)-6].