Enantiospecific Total Synthesis of the Hapalindoles, Fischerindoles, and Welwitindolinones<i>via</i>a Redox Economic Approach

Abstract

Full details are provided for the total synthesis of several members of the hapalindole family of natural products, including hapalindole Q, 12-epi-hapalindole D, 12-epi-fischerindole U, 12-epi-fischerindole G, 12-epi-fischerindole I, and welwitindolinone A. Use of the recently developed direct indole coupling enabled an efficient, practical, scalable, and protecting-group-free synthesis of each of these natural products. The original biosynthetic proposal is reviewed, and a revised biosynthetic hypothesis is suggested, validated by the above syntheses. The syntheses are also characterized by an adherence to the concept of "redox economy". Analogous to "atom economy" or "step economy", "redox economy" minimizes the superfluous redox manipulations within a synthesis; rather, the oxidation state of intermediates linearly and steadily increases throughout the course of the synthesis.