Heterogeneous Photocatalytic Ring Expansion of Cyclic Ketones for the Construction of Medium-Sized Lactams.

Construction of medium-sized ring compounds remains challenging in synthetic chemistry. Herein, we describe the synthesis of medium-sized lactams via a photoinduced ring expansion of benzo-fused cyclic ketones using graphitic carbon nitride (g-C3N4) as a photocatalyst. The ring expansion protocol provided an efficient access to 8-10-membered lactams in good yields and displayed good tolerance to a range of functional groups. The mechanism studies revealed that the photochemical reaction proceeds via an intermediary of a nitrogen radical, which is generated through an oxidative hydrogen atom transfer (HAT) process.

Halogen-Bonding-Promoted C-H Malonylation of Indoles under Visible-Light Irradiation.

Herein, we report a halogen-bonding-based electron donor-acceptor (EDA) complex-promoted photoreaction for the synthesis of C2-malonylated indoles. The protocol provides access to a broad range of functionalized indoles in good yields through the coupling reaction of indoles with diethyl bromomalonate under visible-light irradiation without the need for any transition-metal catalyst or photocatalyst.