Synthesis of tetrahydrofluorenes from the cycloadduct of 3-ethynyl-5-bromo-2-pyrone via cyclocarbopalladation reactions

Cycloadduct from 3-ethynyl-5-bromo-2-pyrone undergoes facile cyclocarbopalladation reactions to provide an array of polycarbocyclic compounds with a complete control of the olefin geometry. Both organotin and boron reagents can be used as a trapping anion source. Treatment of the resulting tetracycles with NaOMe gave rise to various tetrahydrofluorenes in good to excellent isolated yields.