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)