Substrate Encapsulation: An Efficient Strategy for the RCM Synthesis of Unsaturated ϵ-Lactones
摘要:
A facile substrate-encapsulated RCM-based synthesis of 7-membered lactones is reported. Coordination of the alpha,omega-dienyl ester precursor to the bulky Lewis acid (LA) aluminum tris(2,6-diphenylphenoxide) (ATPH) provides a protective extended steric pocket to the olefin moieties, thereby favoring intramolecular RCM over intermolecular ADMET oligomerization. The LA-encapsulated esters undergo ring-closure in the presence of Ru-based olefin metathesis catalysts to give previously difficult-to-access 7-membered beta,gamma- and gamma,delta-unsaturated lactones in good yields.
Escape from Hydrofunctionalization: Palladium Hydride‐Enabled Difunctionalization of Conjugated Dienes and Enynes
作者:Ziyan Zhang、Vladimir Gevorgyan
DOI:10.1002/anie.202311848
日期:2023.11.20
A palladium hydride-catalyzed difunctionalization of dienes and enynes is reported. This mild protocol harnesses visible light to enhance the hydricity of PdH species, enabling a chemoselectivity switch of the hydropalladation step. This method allows for annulation of dienes and enynes with abundant substrates, such as acrylic acids, acrylic amides, and Baylis–Hillman adducts, toward alkenyl or alkynyl
Polysubstituted gamma-lactones are easily obtained, in one step, upon the interaction of bis(TMS)ketene acetals with vicinal allylic acetates in the presence of catalytic amounts of Pd(PPh3)(4). (C) 2008 Elsevier Ltd. All rights reserved.