Photomediated Spirocyclization of N-Benzyl Propiolamide with N-Iodosuccinimide for Access to Azaspiro[4.5]deca-6,9-diene-3,8-dione

Chemodivergent dearomatization of benzene-linked O-oxime esters via EnT-induced radical cross-coupling

Radical-mediated dearomatization strategies offer a blueprint for building value-added and synthetically valuable three-dimensional skeletons from readily available aromatic starting materials. Herein, we report a novel strategy by leveraging benzene-linked O-oxime esters as triply functionalized precursors to form two distinct persistent radicals under a chemodivergent pathway. These radicals then couple with a cyclohexadienyl radical for either carboamination or carbo-aminoalkylation. Remarkably, a series of 4-(2-aminoethyl)anilines derivatives featuring all-carbon quaternary centers, along with the formation of four different types of chemical bonds, are efficiently constructed through a unique rearomatization cascade in the carboamination. Importantly, employing DMPU as the hydrogen atom transfer (HAT) donor strategically diverts the reaction pathway from the C-N bond formation towards the C-C bond formation. Our mechanistic explorations support a sequential HAT/energy transfer (EnT)/HAT cascade as the key stage for carbo-aminoalkylation involving the N-center iminyl radical. Significantly, this work demonstrates the elegant expansion of divergent C-N and C-C bond formation using the imine moiety within O-oxime esters as the bifunctional reagent, and it broadens the chemical space of both benzenes and O-oxime esters in radical-mediated transformations.

Iron(III)-Mediated Nucleophilic Cascade Cyclization of Tertiary Enamides with Diselenides for the Construction of 3-Seleno-2-pyridones

An iron(III)-mediated nucleophilic cascade cyclization of N-propiolyl enamides with various diselenides was developed, which provides an efficient way to construct seleno-heterocycles. A mechanism study shows that the cascade process involves the selective addition of diselenides to the C≡C bond generating a seleniranium ion, followed by an intramolecular nucleophilic attack of enaminic carbon of tertiary enamide. Utilizing this protocol, a variety of 3-seleno-2-pyridones were successfully synthesized featuring good functional group compatibility and simple operation.

Electrosynthesis of Spiro-indolenines via Dearomative Arylation of Indoles in Batch and Continuous Flow

An electrosynthesis of spiro-indolenines in batch and continuous flow was achieved through dearomative arylation of indoles with good functional group compatibility. User-friendly undivided cells were used under catalyst- and oxidant-free conditions. Moreover, the use of a flow electrolysis cell gave high daily productivity and excellent scale-up potential under less supporting electrolyte and higher substrate concentration conditions.

Synthesis of sulfur-containing benzo[b]pyrrolo[2,1-c][1,4]oxazine-3,9-diones: blue light promoted radical cyclization process

The selective and controllable construction of spio-tricyclic skeletons through visible light promoted radical cyclization still remains challenging. Herein, a general and convenient protocol for the blue light-promoted radical-mediated cascade spiro-cyclization/Michael addition of N-arylpropiolamides with thiophenols under metal-free conditions was developed. In this protocol, commercially available hydrochloric acid was employed as the cheap promoter and air as the sustainable oxidant. In addition, many functional groups tolerate the reaction conditions and produce a series of sulfur-containing benzo[b]pyrrolo[2,1-c][1,4]oxazine-3,9-diones.

Tandem Synthesis of 2-Azaspiro[4.5]deca-1,6,9-trien-8-ones Based on Tf2O-Promoted Activation of N-(2-Propyn-1-yl) Amides

Structurally novel 2-azaspiro[4.5]deca-1,6,9-trien-8-ones were synthesized from N-(2-propyn-1-yl) amides and 1,3,5-trimethoxybenzenes by a tandem method consisting of a Tf₂O-promoted amide activation and a TfOH-promoted Friedel-Crafts ipso-cyclization. The method offered the first example of using N-(2-propyn-1-yl) amides as substrates in both Tf₂O-promoted secondary amide activation and the synthesis of azaspiro[4.5]deca-6,9-diene-8-ones.

Multicomponent Direct Assembly of N-Heterospirocycles Facilitated by Visible-Light-Driven Photocatalysis

N-heterospirocycles are interesting structural units found in both natural products and medicinal compounds but have relatively few reliable methods for their synthesis. Here, we enlist the photocatalytic generation of N-centered radicals to construct β-spirocyclic pyrrolidines from N-allylsulfonamides and alkenes. A variety of β-spirocyclic pyrrolidines have been constructed, including drug derivatives, in moderate to very good yields. Further derivatization of the products has also been demonstrated as has a viable scale-up procedure, making use of flow chemistry techniques.