Synthesis of Pyrrolo[2,1‐ a ]isoquinoline Class of Natural Product Crispine A

CuI-Catalyzed Selenylation of Pyrrolo[2,1-a]isoquinolines and Other Electron-Rich Heteroarenes

We have established a mild CuI-catalyzed selenylation of pyrrolo[2,1-a]isoquinoline derivatives in the presence of mCPBA (m-chloroperoxybenzoic acid) at ambient temperature. Corresponding organoselenides have been prepared readily in 53-92% yields. This process can also be expanded to the modification of pyrroles, azaindole, and indoles, delivering the desired heterocyclic selenides in moderate to good yields.

Cascade Synthesis of Pyrrolo[1,2-a]quinolines and Pyrrolo[2,1-a]isoquinolines via Formal [3 + 2]-Cycloaddition of Push-Pull Nitro Heterocycles with Carbonyl-Stabilized Quinolinium/Isoquinolinium Ylides

Various substituted pyrrolo[1,2-a]quinolines and pyrrolo[2,1-a]isoquinolines were synthesized in good to high yields by the Et3N-mediated reaction of push-pull 3-nitrobenzofurans or 1-Ts-/1-Ms-3-nitroindoles and precursors of carbonyl-stabilized quinolinium and isoquinolinium ylides as 1,3-dipole equivalents. These transformations proceed in a one-pot manner starting with the formal [3 + 2]-cycloaddition stage, which is accompanied by double dearomatization of both quinoline/isoquinoline and benzofuran/indole moieties, followed by ring-opening of cyclic intermediate formed and nitrous acid elimination sequence. [3 + 2]-Cycloadducts were isolated as the final products in cases of impossibility or difficulty of their enolization. The present protocol was successfully extended to 3-nitro-4H-chromene derivatives as push-pull dipolarophile component. Finally, using the method of competing reactions, the reactivity of the starting compounds was compared with each other.

TBHP/Et3N-Promoted Chemoselective Formylation and Peroxidation of Pyrrolo[2,1-a]isoquinolines

An efficient formylation of pyrrolo[2,1-a]isoquinoline derivatives has been reached by the use of TBHP (tBuOOH) and Et3N as the mediator. In this strategy, CHO and CDO can be readily incorporated into heteroarenes by the utilization of CHCl3 and CDCl3 as the carbonyl sources. Interestingly, a solvent-controlled chemoselectivity was observed. The use of PhCl as a solvent resulted in dearomatization and peroxidation of pyrrolo[2,1-a]isoquinolines, delivering functionalized peroxides in 53-64% yields.

Pyrrolo[2,1-a]isoquinoline scaffolds for developing anti-cancer agents

Fused pyrrolo[2,1-a]isoquinolines have emerged as compelling molecules with remarkably potent cytotoxic activity and topoisomerase inhibitors. This comprehensive review delves into the intricate world of this family of compounds, analyzing the natural marine lamellarins known for their diverse and complex chemical structures, exploring structure-activity relationships (SARs), and highlighting their remarkable versatility. The review emphasizes their fundamental role as topoisomerase inhibitors and cytotoxic agents, as well as some crucial aspects of the chemistry of pyrrolo[2,1-a]isoquinolines, exploring synthetic strategies in total synthesis and molecular diversification trends, highlighting their importance in the field of medicinal chemistry and beyond.

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.

Environmentally friendly Nafion-catalyzed synthesis of 3-substituted isoquinoline by using hexamethyldisilazane as a nitrogen source under microwave irradiation

This study developed an eco-friendly method to synthesize 3-arylisoquinoline from 2-alkynylbenzaldehydes using Nafion® NR50 as an acidic catalyst and hexamethyldisilazane (HMDS) as a nitrogen source. The reaction proceeded via a 6-exo-dig cyclization under microwave irradiation, giving the corresponding isoquinolines in excellent yields. The advantages of this protocol include: (1) the use of recyclable acid catalysts, (2) transition-metal-free catalysis, and (3) the effective formation of the target product. These features make this methodology a promising approach for the sustainable and efficient synthesis of 3-arylisoquinoline. Some structures were also confirmed by single-crystal X-ray diffraction analysis.

Nitration of Pyrrolo[2,1-a]isoquinolines

We have successfully modified a series of pyrrolo[2,1-a]isoquinolines via direct nitration under mild reaction conditions. Easily accessible nitrates including CAN, Cu(NO₃)₂·H₂O, and Fe(NO₃)₃·9H₂O all can serve as effective nitrating reagents for functionalizing pyrrolo[2,1-a]isoquinolines. Various nitro-bearing pyrrolo[2,1-a]isoquinolines have been efficiently prepared in acceptable to good yields.

Synthesis of Pyrrolo[2,1-a]isoquinolines through Cu-Catalyzed Condensation/Addition/Oxidation/Cyclization Cascade

We have developed a copper-catalyzed synthesis of pyrrolo[2,1-a]isoquinolines with terminal alkynes, aldehydes, and tetrahydroisoquinolines. A variety of pyrrolo[2,1-a]isoquinolines have been prepared in 17-69% yield via a condensation/Mannich-type addition/oxidation/cyclization cascade sequence. Modifications through simple chemical transformations provided highly functionalized molecules containing a privileged framework.

Asymmetric Synthesis of Fused-Ring Tetrahydroisoquinolines and Tetrahydro-β-carbolines from 2-Arylethylamines via a Chemoenzymatic Approach

While chiral fused-ring tetrahydroisoquinoline (THIQ) and tetrahydro-β-carboline (THβC) scaffolds have attracted considerable interest due to their wide spectrum of biological activities, the synthesis of optically pure chiral fused-ring THIQs and THβCs remains a challenging task. Herein, a group of active imine reductases were identified to convert the imine precursors into the corresponding enantiocomplementary fused-ring THIQs and THβCs with high enantioselectivity and conversion, establishing an efficient and green chemoenzymatic approach to fused-ring alkaloids from 2-arylethylamines.

Regiodivergent Synthesis of Methylene and Methyl Ring-Fused Isoquinolinones: Base-Promoted Isomerization of N-Allyl Amides

Methylene and methyl tricyclic isoquinolinones were selectively prepared using a palladium(II)-catalyzed aerobic aza-Wacker reaction, followed by a base- and temperature-controlled Heck reaction catalyzed by palladium(0). Exo- to endo-double-bond migration in isoquinolinones was achieved with 93-99% yields by treatment of the Heck products with Cs₂CO₃ in dimethyl sulfoxide (DMSO) at 150 °C. A probable mechanism for Cs₂CO₃-promoted olefin isomerization was proposed and examined using D-isotope labeling experiments. Finally, yuanamide, a 13-methyl-8-oxoprotoberberine alkaloid, was synthesized using the palladium-catalyzed aza-Wacker/Heck/migration sequence.

Construction of an α-chiral pyrrolidine library with a rapid and scalable continuous flow protocol

The cost-efficient development of an α-chiral pyrrolidine library is achieved via a rapid continuous flow protocol under mild conditions.