Recent developments in the synthesis of the isoquinoline-1,3(2H,4H)-dione by radical cascade reaction

Rhodium-catalyzed C-H activation and three-component tandem annulation leading to isoquinolones

A rhodium-catalyzed C-H activation and three-component coupling of oxazolines, vinylene carbonate and carboxylic acids has been developed. Various isoquinolone products were constructed under redox-neutral conditions with satisfactory yields. It is worth noting that diverse bioactive carboxylic acids have been proven to be effective substrates, and their application in this protocol has expanded the range of isoquinolones with biologically relevant motifs. Multi-dimensional mechanism exploration experiments and derivatization reactions were studied in sequence to explore the details and application prospects of this transformation. It offers an alternative approach for the synthesis of useful isoquinolone derivatives.

Photoinduced Cascade Synthesis of Oxindoles and Isoquinolinediones

Herein, we developed alkyl radical generation from C(sp3)-H bonds of alkanes via a photoinduced HAT-process without employing an external metal, photocatalyst, and organic peroxide. The generated alkyl radical participates in radical addition and cascade cyclization of N-arylacrylamides/N-acryloyl benzamides to deliver structurally diverse and valuable functionalized oxindoles and isoquinolinediones in moderate to good yields. Preliminary mechanistic studies indicated the generation of aryl radical through homolytic cleavage of Ar-I bonds via direct photoexcitation of aryl iodide.

Visible-Light-Driven Bifunctional Photocatalytic Radical-Cascade Selenocyanation/Cyclization of Acrylamides with KSeCN

A visible-light-induced radical-cascade selenocyanation/cyclization of N-alkyl-N-methacryloyl benzamides, 2-aryl-N-acryloyl indoles, and N-methacryloyl-2-phenylbenzimidazoles with potassium isoselenocyanate (KSeCN) was developed. The reactions were carried out with inexpensive KSeCN as a selenocyanation reagent, potassium persulfate as an oxidant, 2,4,6-triphenylpyrylium tetrafluoroborate as a bifunctional catalyst for phase-transfer catalysis, and photocatalysis. A library of selenocyanate-containing isoquinoline-1,3(2H,4H)-diones, indolo[2,1-a]isoquinoline-6(5H)-ones, and benzimidazo[2,1-a]isoquinolin-6(5H)-ones were achieved in moderate to excellent yields at room temperature under visible-light and ambient conditions. Importantly, the present protocol features mild reaction conditions, large-scale synthesis, simple manipulation, product derivatization, good functional group, and heterocycle tolerance.

Photocatalytic Proton-Coupled Electron Transfer Enabled Radical Cyclization for Isoquinoline-1,3-diones Synthesis

Radical cyclization has been demonstrated to be an efficient method to access functionalized heterocycles from easily accessible raw materials. Described herein is the development of a photocatalytic proton-coupled electron transfer (PCET) strategy for the synthesis of isoquinoline-1,3-diones using readily prepared naphthalimide (NI)-based organic photocatalysts. The process features free metal-complex photocatalysts, acids, and mild reaction conditions. This mild radical cyclization protocol has a broad substrate scope and can be effectively applied to a variety of medicinally relevant substrates. Furthermore, control experiments were conducted to elucidate the mechanism of this visible light-induced methodology.

Accessing 3,4-Dihydroquinolinone from N-Arylacrylamides via Tetralone-Mediated Energy Transfer and 1,3-Hydrogen Shift

Herein, we introduce a tetralone-mediated photocyclization method of N-arylacrylamides. The protocol proceeds smoothly to deliver a diverse set of 3,4-dihydroquinolinones in moderate to good yields with excellent functional group compatibility and readily allows for late-stage modifications of a number of complex drug molecules. Mechanistic studies reveal that the present systems with ultraviolet light irradiation enable the cyclization via energy transfer and exclusive 1,3-hydrogen shift.

Diversely functionalized isoquinolines and their core-embedded heterocyclic frameworks: a privileged scaffold for medicinal chemistry

Isoquinoline-enrooted organic small-molecules represent a challenging molecular target in the organic synthesis arsenal attributed to their structural diversity and therapeutic importance. Into the bargain, isoquinolines are significant structural frameworks in modern medicinal chemistry and drug development. Consequently, synthetic organic and medicinal chemists have been intensely interested in efficient synthetic tactics for the sustainable construction of isoquinoline frameworks and their derivatives in enantiopure or racemic forms. This review accentuates an overview of the literature on the modern synthetic approaches exploited in synthesising isoquinolines and their core embedded heterocyclic skeletons from 2021 to 2022. In detail, the methodologies and inspected pharmacological studies for the array of diversely functionalized isoquinolines or their core-embedded heterocyclic/carbocyclic structures involving the introduction of substituents at C-1, C-3, and C-4 carbon and N-2 atom, bond constructions at the C1-N2 atom and C3-N2 atom, and structural scaffolding within isoquinoline compounds have been reviewed. This intensive study highlights the need for and relevance of relatively unexplored bioisosterism employing isoquinoline-based small-molecules in drug design.

Copper(I)-Catalyzed Radical Carbamylation/Cyclization of 2-Aryl-N-methacryloylindoles with Substituted Formamides to Assemble Amidated Indolo[2,1-a]isoquinolin-6(5H)-ones

An efficient synthesis of amidated indolo[2,1-a]isoquinolin-6(5H)-ones has been achieved via copper(I)-catalyzed radical carbamylation/cyclization of 2-aryl-N-methacryloylindoles with substituted formamides. In this reaction, an isoquinoline ring was constructed by carbamylation of a carbon-carbon double bond in 2-arylindoles. This strategy successfully introduces the substituted amide group into the indolo[2,1-a]isoquinoline skeleton and has advantages such as wide substituent scope, mild reaction conditions, high regioselectivity, and good to excellent yields.

A three-component reaction of cyclobutanone oxime esters, sulfur dioxide and N-alkyl-N-methacryloyl benzamides

A three-component reaction of cyclobutanone oxime esters, DABCO·(SO2)2 and N-alkyl-N-methacryloyl benzamides is described. This reaction proceeds without the addition of any oxidant or transition metal, affording sulfonyl-containing isoquinoline-1,3-(2H,4H)-diones in moderate to good yields. Various functional groups are tolerated well in this transformation. Mechanistic studies suggest that a radical pathway is involved, including β-scission, sulfur dioxide insertion, and intramolecular cyclization processes.