Synthesis of Tetrahydrodibenzofuran and Tetrahydrophenanthridinone Skeletons by Intramolecular Nucleopalladation/Oxidative Heck Cascades

Functionalized alkylidene-1,2,3,4-tetrahydrodibenzo[b,d]-furans and -phenanthridin-6(5H)-ones have been synthesized regio- and stereoselectively from either o-iodophenols or -benzamides and alkynes by consecutive Pd-catalyzed Sonogashira coupling and nucleophilic addition/oxidative Heck-type coupling cascade reactions. In the case of iodobenzamide substrates, the whole sequence can be conveniently carried out without the isolation of intermediates. Maleic anhydride has been found to be useful as an additive in the Heck coupling step.