Total syntheses of kealiinines A-C

Abstract

Short total syntheses of the Leucetta-derived alkaloids, kealiinines A-C, have been accomplished using an intramolecular Friedel-Crafts-dehydration sequence of a bis benzylic diol. The precursor diol was obtained through a series of position-specific Grignard reactions from 1-methyl-4,5-diiodoimidazole. C2-Azidation and hydrogenation of the azide then provided the reported structures of kealiinines A-C. While the (1)H NMR data did not completely match for these materials, the HPLC data were consistent with the assigned structure of these alkaloids.

Figure 1. Structures of the Leucetta-family of alkaloids

Figure 2. Putative biosynthetic relationships among the Leucetta alkaloids

Scheme 1. Assembly of the benzimidazole framework (for yields see Table 1)

Scheme 2

Completion of kealiinine A (8a).