Pd(OAc)2-catalyzed domino reactions of 1,2-dihaloarenes and 2-haloaryl arenesulfonates with Grignard reagents: efficient synthesis of substituted fluorenes

Pd(OAc)₂-catalyzed domino reactions of 1,2-dihalobenzenes and 2-haloaryl arenesulfonates with hindered Grignard reagents to form substituted fluorenes, which are believed to occur through palladium associated aryne intermediates, are described. Such palladium associated aryne reaction pathway was found to be favored by omitting the use of phosphine and N-heterocyclic carbene ligands for palladium catalysts and with better leaving groups. Our study suggested that Pd(leaving group)X associated arynes should be formed first and the sp³ C-H activation preferentially occurred at benzylic C-(1°)H bonds. The work described here provides a high yield, one-step access to substituted fluorenes from readily available 1,2-dihalobenzenes and 2-haloaryl arenesulfonates and hindered Grignard reagents, and this substituted fluorene-making method may find applications in the preparation of substituted fluorene-containing molecules including polymers.