A unified approach to benzo[c]phenanthridines via the cascade dual-annulation/formylation of 2-alkynyl/alkenylbenzonitriles

Base-Assisted and Silica Gel-Promoted Indole-Substituted Indene Synthesis

Herein, we report for the first time a transition-metal-free and mild protocol that requires inexpensive K2CO3 and silica gel for direct access to polysubstituted indenes from readily obtainable starting precursors. Notably, sequential Michael addition, intramolecular cyclization, and silica gel-promoted nucleophilic substitution reactions afford the desired products. A broad range of indoles and other aromatic nucleophiles are well-tolerated, affording indenes in moderate to good yields. Gratifyingly, indene could be easily converted into synthetically useful 3-indole-substituted indanone and indanol. Nonetheless, the successful isolation of a reaction intermediate highlights the crucial role of methanol in this reaction.

2-Alkynyl Indole-3-carbonitriles: Synthon for the Regioselective Synthesis of Functionalized 4-Aminocarbazoles

An operationally easy and atom-economical approach for the regioselective tandem synthesis of functionalized 4-aminocarbazoles from easily accessible 2-alkynyl indole-3-carbonitriles under mild reaction conditions has been developed. The developed chemistry involves aza-Henry and successive regioselective annulation to afford the functionalized carbazoles. Replacement of nitromethane with acetophenone led to the formation of the corresponding amino(phenyl)methanone-substituted carbazoles, further extending the diversity of the developed chemistry. The developed methodology accommodates wide functional group variation on the alkyne and is successfully applied for late-stage modification of bioactive molecules.

KOtBu-Promoted [4+2] Annulation-Dehydration Cascade Enabling the Construction of Diverse 2-Pyridone-Fused Uracils

A KOtBu-promoted [4+2] annulation-dehydration cascade reaction has been developed, enabling the efficient synthesis of diverse 2-pyridone-fused uracils through a vinylogous enolization strategy involving o-quinodimethane (oQDM) dienolate intermediates. This method provides a simple yet robust approach for constructing structurally interesting fused N-heterocycles that incorporate two privileged scaffolds, both of which are widely recognized in drug discovery. Consequently, these compounds hold significant potential for biological and pharmacological applications. Moreover, further transformations of the products obtained from this process allow access to highly functionalized and structurally diverse uracil derivatives, expanding the scope of accessible chemical diversity.

Transition-metal free, radical oxidation of 1,6-enyne cyclopropanation: synthesis of aza-bicyclo[4.1.0]heptane derivatives

A straightforward transition-metal-free sustainable methodology for oxidative cyclopropanation of aza-1,6-enynes has been devised, enabling the synthesis of valuable, functionalized azabicyclo[4.1.0]heptane-2,4,5-triones, via four bond formation in a single step under mild conditions. Control experiments and real-time mass data monitoring using online ESI-MS spectroscopy support the pathway proposed for this reaction. The synthesized products have been utilized in diverse product transformations. Key advantages of this reaction include its operational ease, transition metal-free nature, rapid completion, and compatibility with a wide range of functional groups and substrates.

Base-Promoted (5 + 2) Annulation between 2-(Alkynylaryl)acetonitriles and Arylalkynes for the Synthesis of Benzocycloheptene Derivatives

Herein, we describe a novel approach to the synthesis of benzocycloheptene derivatives via base-promoted (5 + 2) annulation between 2-(alkynylaryl)acetonitriles and arylalkynes. In this chemistry, 2-(alkynylaryl)acetonitriles are employed as a new C5 synthon to construct various benzocycloheptene(s) derivatives by building two C-C bonds in one single step. This method features excellent regioselectivity, the use of readily available starting materials, and good functional group tolerance. The practicality of the strategy was further demonstrated by gram-scale synthesis, late-stage functionalizations, and the post-modification of natural products such as probenecid and tetrahydrofurfuryl alcohol.

Alkaline-Metal-Promoted Divergent Synthesis of 1-Aminoisoquinolines and Isoquinolines

Alkaline-metal-promoted divergent syntheses of 1-aminoisoquinolines and isoquinolines have been reported involving 2-methylaryl aldehydes, nitriles, and LiN(SiMe3)2 as reactants. In addition, the three-component reaction of 2-methylaryl nitriles, aldehydes, and LiN(SiMe3)2 has been developed to furnish 1-aminoisoquinolines. This protocol features readily available starting materials, excellent chemoselectivity, broad substrate scope, and satisfactory yields.

Synthesis of Chromenopyrroles (Azacoumestans) from Functionalized Enones and Alkyl Isocyanoacetates

Elegant synthetic strategies for chromenopyrroles (azacoumestans) have been devised via cycloaddition of 2-hydroxychalcone/cyclic enones and alkyl isocyanoacetate, followed by lactonization. Herein, ethyl isocyanoacetate acts as a C-NH-C-C═O synthon contrary to its hitherto applications as a C-NH-C synthon. Subsequently, pentacyclic-fused pyrroles were also constructed from the o-iodo benzoyl chromenopyrroles using the Pd(II) catalyst.