Copper‐Catalyzed 1,2‐Methoxy Methoxycarbonylation of Alkenes with Methyl Formate

• Published in: Angewandte Chemie International Edition 2019-07, Vol.58 (30), p.10305-10309
• Main Authors: Budai, Balázs, Leclair, Alexandre, Wang, Qian, Zhu, Jieping
• Format: Article
• Language: English
• Subjects: Alkenes; Copper; Crystallography; heterocycles; homogeneous catalysis; Lactones; Magnetic resonance spectroscopy; Methyl formate; NMR; NMR spectroscopy; Nuclear magnetic resonance; radicals; Styrene; Styrenes
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201904263

Reported here is a copper‐catalyzed 1,2‐methoxy methoxycarbonylation of alkenes by an unprecedented use of methyl formate as a source of both the methoxy and the methoxycarbonyl groups. This reaction transforms styrene and its derivatives into value‐added β‐methoxy alkanoates and cinnamates, as well as medicinally important five‐membered heterocycles, such as functionalized tetrahydrofurans, γ‐lactones, and pyrrolidines. A ternary β‐diketiminato‐CuI‐styrene complex, fully characterized by NMR spectroscopy and X‐ray crystallographic analysis, is capable of catalyzing the same transformation. These findings suggest that pre‐coordination of electron‐rich alkenes to copper might play an important role in accelerating the addition of nucleophilic radicals to electron‐rich alkenes, and could have general implications in the design of novel radical‐based transformations. A generous donor: Methyl formate acts as a donor of both methoxycarbonyl and methoxy groups in the Cu‐catalyzed alkene difunctionalization reaction. Formation of a diketiminato‐CuI‐styrene ternary complex (1), which was fully characterized, is proposed to accelerate the addition of the nucleophilic methoxycarbonyl radical. TBPA=tert‐butyl peroxyacetate, Tf=trifluoromethanesulfonyl.