Olefin‐Supported Cationic Copper Catalysts for Photochemical Synthesis of Structurally Complex Cyclobutanes

Abstract

The sole method available for the photocycloaddition of unconjugated aliphatic alkenes is the Cu‐catalyzed Salomon–Kochi reaction. The [Cu(OTf)]2⋅benzene catalyst that has been standard in this reaction for many decades, however, is air‐sensitive, prone to photodecomposition, and poorly reactive towards sterically bulky alkene substrates. Using bench‐stable precursors, an improved catalyst system with superior reactivity and photostability has been designed, and it offers significantly expanded substrate scope. The utility of this new catalyst for the preparation of sterically crowded cyclobutane structures is highlighted through the preparation of the cores of the natural products sulcatine G and perforatol.

Photoactive Copper Complexes: Properties and Applications

“…By using [Cu(COD)Cl] 2 in the presence of a catalytic amount of silver hexafluoroantimonate, under UV light, a wide variety of acyclic unconjugated dienes 276 were readily cyclized to the corresponding cyclobutane-fused ring systems 277 with good to excellent yields and moderate to excellent diastereoselectivity, favoring the anti cycloadduct in all cases (Scheme ). The process was found to be remarkably tolerant to several functional groups, including alcohols, amides, chelating and acid-sensitive ethers, or vinyl boronate esters. It is worth noting that the relevant choice of the precatalyst and the additive, especially by using weakly binding counteranions, allowed productive cyclization of some dienes which were not compatible with the original conditions from the Kochi and Salomon groups, which relied on copper(I) triflate as the precatalyst.…”

One-electron bonds in copper–aluminum and copper–gallium complexes

“…lacking sufficient solubility in weakly coordinating solvents. 30–32 Because the BAr F 4 counteranion (BAr F 4 = tetrakis[3,5-bis(trifluoromethyl)-phenyl]borate) confers high solubility in low dielectric solvents, we targeted and isolated [Cu(COD) 2 ]BAr F 4 by protonating the pentameric (CuMes) 5 (ref. 33 and 34) (Mes = 2,4,6-trimethylphenyl) with [(H(OEt 2 ) 2 ]BAr F 4 (ref.…”

“…lacking sufficient solubility in weakly coordinating solvents. [30][31][32] Because the BAr suggested that {CuM} 11 complexes are accessible at low potentials (Fig. S31-36 †).…”

Strategic Use of Visible-Light Photoredox Catalysis in Natural Product Synthesis

“…The dimerization of unsubstituted styrenes is especially challenging, as they are prone to polymerization. As a result, the synthesis of (±)-pellucidin A (19) was carried out at low temperature and was less efficient. The critical role played by the relay oxidant was highlighted by resubjecting cyclodimer 18 to photocatalytic conditions and observing that it suffered significant cycloreversion if anthracene was omitted.…”

“…Therefore, photocatalysts with high extinction coefficients at wavelengths >400 nm are particularly well-suited for synthetic applications. Nevertheless, it should be noted that UV irradiation can also lead to efficient and selective photocatalyzed reactions if care is taken to ensure there is no absorption of the reaction components in the region of irradiation. − …”