Total Synthesis of (±)-Impatien A via Aza-Heck Cyclization

Brønsted-Acid Catalyzed Diastereo- and Enantioselective Synthesis of Spiroisoindolinones from Enamides

A highly stereoselective Brønsted-acid catalyzed synthesis of densely substituted spiroisoindolinones from enamides and 3-hydroxy-isoindolinones is described. With simple Brønsted-acids, such as para-toluene sulfonic acid, spiroisoindolinones with three contiguous stereogenic centers are formed in high yields (up to 97 %) and diastereoselectivities (up to >98 : <2 : 0 : 0 dr) under mild reaction conditions. With the use of a chiral phosphoric acid catalyst, a diastereo- and enantioselective synthesis of the corresponding spiroisoindolinones was achieved. Mechanistic investigations indicate a step-wise mechanism via an initial addition of the enamide to an electrophilic N-acylimine species followed by an intramolecular aza-Friedel-Crafts reaction. Addition of a strong Lewis acid can be used to facilitate the second step for less reactive substrates.

Enantioselective Synthesis of Isoindolinone by Sequential Palladium-Catalyzed Aza-Heck/Suzuki Coupling Reaction

We present a tandem aza-Heck/Suzuki cross-coupling reaction of O-phenyl hydroxamic ethers with readily available arylboronic and alkenyl boronic acids. This protocol is enabled by a palladium catalyst paired with chiral phosphoramidite ligands, particularly under mild reaction conditions, yielding efficient and succinct synthetic routes to chiral isoindolinones with high enantioselectivity. Furthermore, this reaction exhibits excellent functional group compatibility and a rich diversity of subsequent transformations.

Synthesis of C-N or C-C Spiroindolines via Rearrangement Coupling Reaction

Herein, we report a general approach to effectively construct C-N or C-C spiroindolines using tetrahydro-β-carbolines as starting materials via a rearrangement coupling reaction. This method is characterized by its operational simplicity and mild conditions. Notably, a wide range of anilines and indoles are suitable for this intermolecular coupling, yielding the corresponding C-N or C-C spiroindolines in good to excellent yields.

Brønsted Acid-Catalyzed Diastereoselective Synthesis of Spiroisoindolinones from Enamides

A highly diastereoselective synthesis of spiroisoindolinones from enamides and 3-hydroxy-isoindolinones is reported. The reaction proceeds rapidly in the presence of p-toluenesulfonic acid as a Brønsted acid catalyst and affords a variety of densely substituted spiroisoindolinones with three contiguous stereogenic centers in high yields (≤98%) and diastereoselectivities (up to dr >98:<2:0:0).

Towards a General Access to 1-Azaspirocyclic Systems via Photoinduced, Reductive Decarboxylative Radical Cyclizations

A convenient and versatile approach to important 1-azaspirocyclic systems relevant to medicinal chemistry and natural products is reported herein. The main strategy relies on a reductive decarboxylative cyclization of redox-active esters which can be rapidly assembled from abundant cyclic azaacids and tailored acceptor sidechains, with a focus on alkyne acceptors enabling the generation of useful exo-alkene moieties. Diastereoconvergent variants were studied and could be achieved either through remote stereocontrol or conformational restriction in bicyclic carbamate substrates. Two sets of metal-free photocatalytic conditions employing inexpensive eosin Y were disclosed and studied experimentally to highlight key mechanistic divergences.

Cyclopropane-Fused N-Heterocycles via Aza-Heck-Triggered C(sp3)-H Functionalization Cascades

Unique examples of aza-Heck-based C(sp³)–H functionalization cascades are described. Under Pd(0)-catalyzed conditions, the aza-Heck-type cyclization of N-(pentafluorobenzoyloxy)carbamates generates alkyl–Pd(II) intermediates that effect C(sp³)–H palladation en route to cyclopropanes. Key factors that control the site selectivity of the cyclopropanation process have been elucidated such that selective access to a wide range of ring- or spiro-fused systems can be achieved.

Selected Ion Monitoring Using Low-Cost Mass Spectrum Detectors Provides a Rapid, General, and Accurate Method for Enantiomeric Excess Determination in High-Throughput Experimentation

High-Throughput Experimentation (HTE) workflows are efficient means of surveying a broad array of chiral catalysts in the development of catalytic asymmetric reactions. However, use of traditional HPLC-UV/vis methodology to determine enantiomeric excess (ee) from the resulting reactions is often hampered by co-elution of other reaction components, resulting in erroneous ee determination when crude samples are used, and ultimately requiring product isolation prior to ee analysis. In this study, using four published reactions selected as model systems, we demonstrate that the use of LC-MS, SFC-MS, and selected ion monitoring (SIM) mass chromatography provides a highly accurate means to determine ee of products in crude reaction samples using commonplace, low-cost MS detectors. By using ion selection, co-eluting signals can be deconvoluted to provide accurate integrations of the target analytes. We also show that this method is effective for samples lacking UV/vis chromophores, making it ideal for HTE workflows in asymmetric catalysis.