Regioselectivity Switch in Palladium−Catalyzed Allenylic Cycloadditions of Allenic Esters: [4+1] or [4+3] Cycloaddition/Cross‐Coupling by Ligands

The first Pd‐catalyzed asymmetric allenylic [4+1] cycloaddition was successfully developed. Alternatively, tuning Pd catalysts switched the reactivity toward an unprecedented [4+3] cycloaddition/cross coupling. Ligands play a vital role in controlling the reaction pathway, allowing highly selective access to different products from identical substrates. Biological evaluation of the obtained compounds led to the discovery of new good antitumor targets. A possible mechanism was proposed, suggesting two interesting catalytic cycles for the cycloaddition with palladium−butadienyls. This study also demonstrated the potential and utility of allenic esters as 1,4‐biselectrophiles and C4 synthons for participating in cycloaddition reactions

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