A stepwise dearomatization/nitration/enantioselective homoenolate reaction of quinolines to construct C3-nitro-substituted tetrahydroquinolines

Herein, we describe a stepwise 1,2-reductive dearomatization/selective C3-nitration of quinoline and a subsequent catalytic enantioselective homoenolate addition reaction using a NHC catalyst strategy to construct N-acetyl 3,4-disubstituted tetrahydroquinoline in good yields with remarkably high diastereo- and enantioselectivities (dr >99 : 1, ee up to >99%). An efficient metal- and base-free method for 3-nitroquinoline synthesis from readily accessible quinoline has also been realized.

Isocyanide-based multicomponent reactions for the synthesis of benzopyran derivatives with biological scaffolds

Benzopyrans (BZPs) are among the most privileged and influential small O-heterocycles that form the core of many natural compounds, commercial drugs, biological compositions, agrochemicals, and functional materials. BZPs are divided into six general categories including coumarins, chromans, 2H-chromenes, 4H-chromenes, chromones, and 4-chromanones, each of which is abundant in many plants and foods. These oxygenated heterocyclic compounds are fascinating motifs and have extensive applications in biology and materials science. Hence, numerous efforts have been made to develop innovative approaches for their extraction and synthesis. However, most of them are step-by-step or multi-step strategies that suffer from waste material generation and a tedious extraction process. Isocyanide-based multicomponent reactions (I-MCRs) offer a highly efficient method for overcoming these problems. The I-MCR is a simple and environmentally friendly one-pot domino procedure that does not require intermediate isolation or workup and is generally more efficient in material usage. This review covers all research articles related to I-MCRs for synthesizing BZP derivatives from the beginning to the middle of the year 2023. This strategy will be useful for organic and pharmaceutical chemists to design new drugs and optimize the synthesis steps of biological compounds and commercial drugs with benzopyran cores.

Synthesis of Trisubstituted Chromanes by Lewis-Base-Catalyzed Three-Component Electrophilic Thiofunctionalization of Cyclopropene with Phenols via a Formal [3 + 3] Annulation

A Lewis-base-catalyzed three-component electrophilic thiofunctionalization of cyclopropene with phenol is developed to furnish various trisubstituted chromanes in high trans-diasteroselectivity. This metal-free protocol is easy to scale-up, offers a unique 2,2,3-substitution pattern, and delivers chromanes with diversified core substitution patterns. The unprecedented tolerance of strong electron-withdrawing substituents at the phenol renders the protocol indispensable to access the otherwise inaccessible chromane chemical space that is important for medicinal chemistry campaigns.

Highly diastereoselective annulation of 2-substituted 3-nitro-2H-chromenes with hemicurcuminoids and curcuminoids via a double and triple Michael reaction cascade

The K2CO3-catalysed double Michael addition of (E)-1,5-diaryl- and 1-alkyl-5-arylpent-4-ene-1,3-diones to 2-trifluoromethyl- and 2-phenyl-substituted 3-nitro-2H-chromenes in dichloromethane at room temperature for 48 h results in 10-aroyl(acyl)-7-aryl-6a-nitro-6,6a,7,8,10,10a-hexahydro-9H-benzo[c]chromen-9-ones in 75-98% yields as individual...

N-Heterocyclic carbene-catalysed homoenolate addition reaction to 3-cyano-2-imino-2H-chromenes: synthesis of C4-functionalized 2-amino-3-cyano-4H-chromene

A NHC-catalyzed homoenolate addition reaction between enals and iminochromenes to yields of a new type of C4-functionalized 2-amino-4H-chromenes has been developed.

Synthesis of 5H-chromeno[3,4-b]pyridines via DABCO-catalyzed [3 + 3] annulation of 3-nitro-2H-chromenes and allenoates

The DABCO-catalyzed [3 + 3] annulation between 3-nitro-2H-chromenes and benzyl 2,3-butadienoate has been developed as a route to 5H-chromeno[3,4-b]pyridine derivatives. Under optimal reaction conditions, 5H-chromeno[3,4-b]pyridines incorporating two allenoate units were obtained in moderate to good yields (30-76%). The same type of transformation could be carried out using butynoates as allene surrogates. Mechanistic studies by mass spectrometry allowed the identification of the key intermediates involved in the reaction mechanism. The reported synthetic methodology represents an entirely new approach for the synthesis of the 5H-chromeno[3,4-b]pyridine core structure based on allene chemistry.

Access to Optically Enriched α-Aryloxycarboxylic Esters via Carbene-Catalyzed Dynamic Kinetic Resolution and Transesterification

Optically active α-aryloxycarboxylic acids and their derivatives are important functional molecules. Disclosed here is a carbene-catalyzed dynamic kinetic resolution and transesterification reaction for access to this class of molecules with up to 99% yields and 99:1 er values. Addition of a chiral carbene catalyst to the ester substrate leads to two diastereomeric azolium ester intermediates that can quickly epimerize to each other and thus allows for effective dynamic kinetic resolution to be realized. The optically enriched ester products from our reaction can be quickly transformed to chiral herbicides and other bioactive molecules.

Synthesis of 2H-Chromenes via Unexpected [4 + 2] Annulation of Alkynyl Thioethers with o-Hydroxybenzyl Alcohols

A novel Brønsted acid-catalyzed reaction of alkynyl thioethers with o-hydroxybenzyl alcohols via an unexpected formal [4 + 2] annulation has been developed. This metal-free protocol leads to the facile and practical synthesis of valuable polysubstituted 2H-chromenes in mostly good to excellent yields under mild reaction conditions and features a wide substrate scope and excellent functional group tolerance.