Allyl Monitorization of the Regioselective Pd-Catalyzed Annulation of Alkylnyl Aryl Ethers Leading to Bismethylenechromanes.

The mechanism for the synthesis of 2,3-bismethylenechromanes obtained by the reaction between silylethynyloxyarenes and allylic pivalates and catalyzed by a palladium complex has been investigated using computational methods rooted in density functional theory. The reaction is promoted by a C-H bond activation and the consequent bond cleavage of both substrates, followed by a novel annulation. The whole mechanism of this reaction is described together with the drawbacks that could block it. The main role played by the allyl rotation, inducing selectivity, together with the lability of the phosphine ligand and base (Cs2CO3) effects are unraveled. Finally, the nature of the substrates was managed, confirming that ortho-allylated silylethynyloxybenzenes lead to the same type of annulated products.