Synthetic studies on indoles and related compounds. Part 46.1 First total syntheses of 4,8-dioxygenated β-carboline alkaloids

Total syntheses of naturally occurring 4,8-dioxygenated β-carboline alkaloids 2a, 2d, 2g, and 2h are described. The synthetic route involves two methodologies that we developed; (i) an improved Fischer indolization for the synthesis of a 7-oxygenated indole using a tosyl group for protection of the phenolic group, (ii) construction of a 4-methoxy-β-carboline skeleton by the C-3-selective cyclization of the C-2-substituent of the indole nucleus. The phenolic O-tosyl group of the β-carboline skeleton was successfully cleaved to the phenol by Na-anthracenide, and this phenol was methylated with TMSCH2N2.