Sequential Suzuki-Miyaura Coupling/Lewis Acid-Catalyzed Cyclization: An Entry to Functionalized Cycloalkane-Fused Naphthalenes

A Visible Light Ru-Catalyzed Photoredox Access to Substituted Dihydrofurans

An efficient, visible light Ru(bpy)₃Cl₂-catalyzed method for the preparation of 2,3-dihydrofurans is reported. This approach employs 2-bromoketoesters as radical precursors and alkyl enol ethers as acceptors. The photoredox cycle furnishes an oxonium ion that is captured by an internal nucleophile to render the corresponding dihydrofurans. Moreover, the obtained products contain a versatile acetal moiety at C-2, allowing its transformation into a diverse variety of heteroaromatic and nonaromatic compounds. This method could serve as an important tool in the synthesis of complex tetrahydro- and dihydrofurans as well as heteroaromatic structures.

Tf2O-Mediated Cyclization of 7-Enamides: Bioinspired Construction of Fused Eight-Membered Carbocyclic Enimines and Enones

In this paper, we document the construction of functionalized and fused eight-membered carbocycles by the triflic anhydride-mediated cyclization of 7-enamides. Taking advantage of the high electrophilicity of the nitrilium ion intermediates, generated in situ from secondary N-(2,6-dimethyl)anilides, the nonactivated, trisubstituted alkene-nitrilium cyclization reactions proceeded smoothly to afford nonconjugated β,γ-enimines (for fused 6/6/8 ring systems), conjugated α,β-enimines (for 6/5/8), or fused 5/8 ring systems in good yields. When the cyclization reactions were followed by one-pot acidic hydrolysis, the reaction led directly to the corresponding α,β-enones. For some substrates, the reaction afford an efficient access to pendent cyclic β,γ-enimines/enones.