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.