Functionalized Phenanthridine and Dibenzopyranone Derivatives through Benzyne Cyclization – Application to the Total Syntheses of Trisphaeridine and N‐Methylcrinasiadine

A series of regioselectively functionalized benzo[c]chromen‐6‐ones, phenanthridinones, and phenanthridine derivatives have been prepared by an anionic cyclization and in situ oxidation sequence starting from 2‐bromobenzyl‐2‐fluorophenyl ethers and amines. These processes involve the generation of a benzyne‐tethered aryllithium intermediate and subsequent 6‐exo‐dig cyclization. By applying this methodology to the appropriate starting materials, short and efficient syntheses of Amaryllidaceae alkaloids trisphaeridine and N‐methylcrinasiadine have been achieved in good overall yields. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)