Palladium-Catalyzed Cross-Coupling, Divergent Allene Generation, and Cycloadditions toward Cyclobuta[b]naphthalen-3(1H)‑ones and 11H-Benzo[b]fluoren-11-ones

The Pd-catalyzed reaction of 1-(2-iodophenyl)-3-arylprop-2-yn-1-ones with propargyl sulfonamide produces cyclobuta[b]naphthalen-3(1H)-ones, while the reaction of 1-(2-iodophenyl)-3-arylprop-2-yn-1-ones with propargyl ethers under the similar palladium catalysis affords 11H-benzo[b]fluoren-11-ones as products. Combined experimental and theoretical studies on the reaction mechanism reveal that the former reaction proceeds through the Pd-catalyzed cross-coupling, propargyl-allenyl isomerization (1,3-H transfer) and [2 + 2] cycloaddition, whereas the latter involves a process of Pd-catalyzed cross-coupling, a propargylic Alder-ene-type reaction (1,8-H transfer) and 6π-electrocyclization leading to the formation of the formal [4 + 2] cycloadducts. The divergent formation of two types of allenic intermediates depending on propargylic substrates is confirmed and elucidated.