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)