Site-Selective Arylation of Naphthalenes: a Key Entry towards Extended Fluorenones and Phenanthridinones

The development of an oriented arylation process dedicated to the naphthalene core is presented. Our approach is based on dual role of N-tosyl carboxamides acting jointly as a directing group in a first C-H arylation step and as a CO or CO-NH fragment precursor in a further construction step of naphthalene-based fluorenone or phenanthridinone derivatives. The presence of the directing group in position 1 and 2 of the naphthalene platform allowed selective arylations in position 2 and 3 respectively. Our study represents a first synthetic and general entry of C-H arylation at naphthalene platforms towards the preparation of extended fluorenones as well as benzo-fused phenanthridinones. Further, the C-H arylation and cyclisation sequence represents a useful way to the preparation of novel extended tetra- and pentacyclic fluorenones bearing both electron donating as well as electron withdrawing groups in various substitution patterns. Additionally, both the regioselectivity and the reaction paths of the cyclization leading to the fluorenone architectures was studied by DFT calculations which fully complement experimental observations.