Hauser-Kraus Annulation Initiated Multi-Cascade Reactions for Facile Access to Functionalized and Fused Oxazepines, Carbazoles and Phenanthridinediones

The Hauser-Kraus (H-K) annulation of N-unsubstituted 3-olefinic oxindoles with 3-nucleophilic phthalides triggers a cascade of ring expansion and ring contraction reactions through several regioselective steps in one pot. While oxazepines were isolated in the presence of stoichiometric amounts of base at room temperature, carbazoles and phenanthridinediones were the products in the presence of excess base and microwave irradiation. Mechanistic studies guided by stepwise reactions and control experiments revealed that the isolable oxazepine intermediate, formed via ring expansion of the H-K adduct, is the key precursor to carbazole and phenanthridinedione via decarboxylative regioselective cyclizations.

A Cascade Reaction of Michael Addition and Truce-Smiles Rearrangement to Synthesize Trisubstituted 4-Quinolone Derivatives

A novel transition-metal-free cascade reaction to synthesize 4-quinolone derivatives has been demonstrated. Michael addition and Truce-Smiles rearrangement are included in this protocol, providing a broad scope of 4-quinolones in moderate-to-excellent yields. This work serves as an example of the use of sulfonamides through Truce-Smiles rearrangement to build heterocyclic compounds under mild conditions.

Palladium-catalyzed regio- and stereoselective access to allyl ureas/carbamates: facile synthesis of imidazolidinones and oxazepinones

Typically, transition metal catalysis enforces the stereodefined outcome of a reaction. Here we disclose the palladium-catalyzed regio- and stereoselective access to allylic ureas/carbamates and their further exploitation to diverse cyclic structures under operationally simple reaction conditions. This protocol features palladium-catalyzed decarboxylative amidation of highly modular VECs with good to excellent yield, minimal waste production, wide substrate scope, and low catalyst loading. In follow-up chemistry, we demonstrated the debenzylation of vinylic imidazolidinones to N-hydroxycyclic ureas and regioselective derivatization towards the facile synthesis of halohydrins and oxiranes under mild reaction conditions in good to excellent yields.

Calcium-catalyzed reactions of element-H bonds

Investigation on organocalcium catalysis is just unfolding during the past decade. Beside conventional Ca salts with strong electron-withdrawing counter anions that may serve as Lewis acid catalysts, many Ca complexes have also been designed recently and found to be good catalysts in activation of element-H (EH) bonds like transition metal catalysts. These findings are interesting and may attract the interest of the chemists. Due to the great abundance, non-toxicity, and biocompatible features of Ca element, Ca-catalyzed reactions can be of great significance from the viewpoint of industry. This short review summarizes the recent advances on Ca-catalyzed reactions of EH bonds. We hope that it may provide a useful guide for interested readers from both the academy and industry.