Palladium-Catalyzed Cross-Coupling, Divergent Allene Generation, and Cycloadditions toward Cyclobuta[<i>b</i>]naphthalen-3(1<i>H</i>)-ones and 11H-Benzo[<i>b</i>]fluoren-11-ones
Shugao Zhu, Dan Wang, Shihan Liu, Yufeng Ma, Hong Wang, Yu Lan, Ruopeng Bai, Ruwei Shen
Abstract
The Pd-catalyzed reaction of 1-(2-iodophenyl)-3-arylprop-2-yn-1-ones with propargyl sulfonamide produces cyclobuta[ b ]naphthalen-3(1 H )-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.