Regioselectivity Switch in Palladium-Catalyzed Allenylic Cycloadditions of Allenic Esters: [4+1] or [4+3]
Long Li1, Pengfei Luo1, Yuhua Deng1
1Key Laboratory of Medicinal Chemistry for Natural Resource, Ministry of Education, School of Chemical Science and Technology, State Key Laboratory for Conservation and Utilization of Bio-Resources in Yunnan, Yunnan University, Kunming, 650091, China.
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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