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

Switch it: The use of metal‐butadienyl species in a cycloaddition is exemplified by the first Pd‐catalyzed asymmetric allenylic [4+1] cycloaddition. Notably, tuning the Pd catalysts switched the reactivity toward an unprecedented [4+3] cycloaddition/cross‐coupling. These reactions lead to diverse and valuable carbocycles and heterocycles, and also provide a straightforward synthesis to [3]dendralenes.

Abstract

The first Pd‐catalyzed asymmetric allenylic [4+1] cycloaddition was successfully developed. Alternatively, tuning the Pd catalyst 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 antitumor targets. A possible mechanism is 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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