Synthesis Of Isoquinolines Research Articles

Rapid and Atom Economic Synthesis of Isoquinolines and Isoquinolinones by C–H/N–N Activation Using a Homogeneous Recyclable Ruthenium Catalyst in PEG Media

Herein, we report an atom‐efficient, rapid, green, and sustainable approach to synthesize isoquinolines and isoquinolinones using a homogeneous recyclable ruthenium catalyst in PEG Media assisted by microwave energy. Dibenzoylhydrazine was used for C–H/N–N activation reactions for the first time in combination with ketazine as oxidizing directing groups for annulation reactions with internal alkynes. The developed protocol is environmentally benign due to significantly shortened times with an easy extraction method, higher atom economy, external oxidant and silver or antimony salt free conditions, applicability to a gram scale synthesis, use of biodegradable solvent and wide substrate scope with higher product yields. Moreover, it is worth noting that the established methodology allowed reuse of the catalytic system for up to five successive runs with minimal loss in activity.

Ruthenium-Catalyzed Annulation of N-Cbz Hydrazones via C–H/N–N Bond Activation for the Rapid Synthesis of Isoquinolines

In this work, N-Cbz hydrazone has been employed as a rarely explored directing group for the synthesis of isoquinolines by annulation with internal alkynes via C–H/N–N activation using Ru catalyst. Additive as well as external oxidant-free rapid protocol has been established for the synthesis of isoquinolines using microwave strategy. Use of non-volatile and biodegradable PEG as a green solvent with lower catalyst loading makes the proposed protocol environmentally benign. Further, higher functional group tolerance and wide substrate scope has been observed under the stated methodology with higher yields.

Acoustic Droplet Ejection Enabled Automated Reaction Scouting.

Miniaturization and acceleration of synthetic chemistry are critically important for rapid property optimization in pharmaceutical, agrochemical, and materials research and development. However, in most laboratories organic synthesis is still performed on a slow, sequential, and material-consuming scale and not validated for multiple substrate combinations. Herein, we introduce fast and touchless acoustic droplet ejection (ADE) technology into small-molecule chemistry to transfer building blocks by nL droplets and to scout a newly designed isoquinoline synthesis. With each compound in a discrete well, 384 random derivatives were synthesized in an automated fashion, and their quality was monitored by SFC-MS and TLC-UV-MS analysis. We exemplify a pipeline of fast and efficient nmol scouting to mmol- and mol-scale synthesis for the discovery of a useful novel reaction with great scope.

Tuneable access to isoquinolines via a transition-metal-free C(sp3)–C(sp3) bond cleavage rearrangement reaction

A novel divergent synthesis of multi-substituted isoquinolines via C(sp3)–C(sp3) bond cleavage rearrangement reactions was realized.

Tunable synthesis of quinolinone-fused isoquinolines through sequential one-pot nucleophilic addition and palladium-catalyzed intramolecular C-H alkenylation.

An efficient sequential one-pot synthesis of fused heterocycles based on 4-quinolinone and isoquinoline scaffolds of biological interest has been developed. In all cases, the first nucleophilic addition of 2-aryl quinolin-4(1H)-ones to alkynyl bromides in tert-pentyl alcohol can proceed in a chemo-, regio- and stereoselective manner to give (Z)-N-(1-bromo-1-alken-2-yl)quinolin-4-ones at 110 °C. Sequentially, these in situ functionalized adducts can undergo direct intramolecular aromatic C-H alkenylation in the presence of PdCl2 (5 mol%) in mixed solvents (tert-pentyl alcohol/DMF = 1 : 1), affording the novel quinolinone-fused isoquinoline derivatives in good yields.

Cp*Co(iii)-catalyzed annulation of azines by C-H/N-N bond activation for the synthesis of isoquinolines.

Herein, an efficient, atom economic and external oxidant free approach has been disclosed for the synthesis of isoquinolines. Azines were employed for annulation reactions with alkynes via sequential C-H/N-N bond activation using an air-stable cobalt catalyst. The method takes advantage of the incorporation of both the nitrogen atoms of azines into the desired isoquinoline products, offering the highest atom economy. In addition, the developed protocol works under external oxidant as well as silver salt free conditions. Furthermore, the established methodology features a relatively broad substrate scope with high product yields and scalability up to the gram level.

Synthesis of Isoquinoline from Benzimidates via Ru(II)‐Catalyzed C–H Alkylation/Annulations with Diazo Compounds

AbstractA Ru(II)‐catalyzed C–H alkylation/annulations of benzimidate with diazo compounds have been developed for the synthesis of functionalized isoquinoline. The reaction proceeds under mild condition and exhibit broad functional group tolerance. This strategy also provides a direct approach to isoquinolines and 3,4‐dihydrophenanthridin synthesis. Moreover, Ru(II)‐catalyzed C−H carbenoid functionalization of benzimidate with diazodiester is also demonstrated.

Synthesis of Indole-Dihydroisoquinoline Sulfonyl Ureas via Three-Component Reactions

Isoquinolines activated with sulfamoyl chlorides were reacted with indoles in a 3-component reaction to generate a library of dihydroisoquinoline derivatives. Using a differential protecting group strategy, products could be further derivatised. Synthesis of isoquinoline starting materials using several different methods is also described.

Air-Stable CpCoI-Phosphite-Fumarate Precatalyst in Cyclization Reactions: Comparing Different Methods of Energy Supply.

The robust CoI precatalyst [CpCo(P{OEt}3)(trans‐MeO2CHC=CHCO2Me)] was investigated in cyclotrimerizations, furnishing benzenes and pyridines from triynes, diynes and nitriles, comparing the influence of different ways of energy supply; namely, irradiation and conventional (thermal) or microwave heating. The precatalyst was found to work under all conditions, including the possibility to catalyze cyclotrimerizations at room temperature under photochemical conditions at longer reaction times. Performance of the reactions in a microwave reactor proved to be the most time‐efficient way to rapidly assemble the expected reaction products; however, careful selection of reaction conditions can be required. The synthesis of pyridines and isoquinolines successfully involved the utilization of versatile functionalized nitriles, affording structurally interesting reaction products. Comparison with the known and often applied precatalyst CpCo(CO)2 demonstrated the significantly higher reactivity of the CpCoI–phosphite–olefin precatalyst.

Synthesis of Isoquinolines through IrIII‐Catalyzed C–H Activation/Annulation from Benzimidates with Hydroxylisopropylalkynes

An IrIII‐catalyzed cascade reaction consisting of C–H activation/annulation of benzimidates with hydroxylisopropylalkynes is reported. A broad range of isoquinolines has been prepared in one step with good functiona‐group tolerance and high efficiency.

Highly Regioselective Isoquinoline Synthesis via Nickel‐Catalyzed Iminoannulation of Alkynes at Room Temperature

A simple and cost‐efficient nickel catalytic system for the annulation of 2‐haloaldimines with alkynes to synthesize 3,4‐disubstituted and 3‐substituted isoquinolines at room temperature has been developed. The air‐stable and inexpensive Ni(dppe)Cl2 was employed as a precatalyst, and Et3N was found to be an essential additive for obtaining high yields. By using this nickel catalytic system one‐pot three‐component direct synthesis of isoquinolines starting with simple 2‐halobenzaldehydes, tert‐butylamine, and alkynes were also achieved. These reactions occur in moderate to excellent yields with complete regioselectivity. Moreover, these reactions feature a broad substrate scope, easy scalability, operational simplicity, and excellent practicality.

Isoquinoline synthesis by C-H activation/annulation using vinyl acetate as an acetylene equivalent

Vinyl acetate is used as an acetylene equivalent in rhodium(III)-catalysed C-H activation/annulation with aryl ketoxime esters. Extension to an aldoxime ester allows for a concise formal synthesis of decumbenine B.

Visible-Light Photoredox-Catalyzed Iminyl Radical Formation by N-H Cleavage with Hydrogen Release and Its Application in Synthesis of Isoquinolines.

An unprecedented visible-light photoredox-catalyzed iminyl radical formation by N-H cleavage with H2 release has been developed. Its application in the synthesis of various isoquinolines and related polyaromatics in high atom economy at ambient temperature by applying a photosensitizer, Acr+-Mes ClO4-, and a new cobalt catalyst, Co(dmgH)2(4-CONMe2Py)Cl is reported. Mechanistic investigations indicated that the generated iminyl radical initiates the cascade C-N/C-C bonds formation and the catalytic cycle occurs by a simultaneous oxidative as well as reductive quenching pathway.

Palladium-Catalyzed α-Arylation of Silylenol Ethers in the Synthesis of Isoquinolines and Phenanthridines.

A diverse array of isoquinolines and phenanthridines have been accessed by developing a two-step, one-pot method constituting regioselective palladium-catalyzed Kuwajima-Urabe α-arylation of silylenol ethers and acid-mediated deprotection, annulation, and aromatization. Structural diversity in the silylenol ethers leads to three different classes of isoquinolines and phenanthridines from which related natural products can be derived. The synthetic utility of this method by the quick assembly of the natural product trispheridine is also demonstrated.

Synthesis of Polysubstituted Isoquinolines and Related Fused Pyridines from Alkenyl Boronic Esters via a Copper-Catalyzed Azidation/Aza-Wittig Condensation Sequence.

An efficient and straightforward synthesis of isoquinolines is reported from internal alkenyl boronic esters, easily prepared from the corresponding 1,2-bis(boronates), via a sequential copper-catalyzed azidation/aza-Wittig condensation. This synthetic method has been used to synthesize quinisocaine, a topical anesthetic used for the treatment of pain and pruritus, and further extended to thieno[2,3-c]pyridines by using 2-thiophenecarboxaldehyde as coupling partner in the first step.

N-Tosylhydrazone directed annulation via C-H/N-N bond activation in Ru(ii)/PEG-400 as homogeneous recyclable catalytic system: a green synthesis of isoquinolines.

A green and sustainable methodology for the synthesis of isoquinolines using Ru(ii)/PEG-400 as a homogeneous recyclable catalytic system has been demonstrated. N-Tosylhydrazone, a rarely explored directing group, has been successfully employed for an annulation type of reaction with alkynes via C-H/N-N activation. A short reaction time with a simple extraction procedure, a wide substrate scope with high yields of products, easily prepared substrates, biodegradable solvent, and scalability up to the gram level enhance the efficiency and sustainability of the proposed protocol. Further, the expensive ruthenium-based homogeneous catalytic system could be reused up to a fourth consecutive cycle without any loss in its activity.

Tandem radical cyclization for the construction of 1-difluoroalkylated isoquinolines via Cu catalyzed and visible light-promoted pathways

A Cu/B2pin2 system promoted cyclization for the synthesis of 1-difluoroalkylated isoquinolines with vinyl isocyanides and bromodifluoroacetic derivatives in moderate to good yields was reported. This method provided a mild and efficient pathway for the construction of diverse 1-difluoroalkylated isoquinolines via a proposed tandem radical cyclization process.

Synthetic access to isoxazoline-functionalized isoquinolines via microwave-assisted iminoxyl radical-participated cascade cyclization of vinyl isocyanides.

A convenient microwave-assisted method for the synthesis of isoxazoline-functionalized isoquinolines via the n-Bu4NI (TBAI) catalyzed radical cascade cyclization of vinyl isocyanides with β,γ-unsaturated ketoximes has been described. The methodology presented here achieves a wide substrate scope and good to excellent yields. A radical mechanism is proposed, which is supported by the intermolecular competing kinetic isotope effect (KIE) experiment and the radical trapping experiment.

Pomeranz-Fritsch Synthesis of Isoquinoline: Gas-Phase Collisional Activation Opens Additional Reaction Pathways.

We have investigated the gas-phase production of isoquinoline by performing collisional activation on benzalaminoacetal, the first intermediate in the classic solution-phase Pomeranz-Fritsch synthesis of isoquinoline. We have elucidated the reaction pathways in the gas phase using tandem mass spectrometry. Unlike the corresponding condensed-phase reaction, where catalytic proton exchange between intermediate(s) and solvent (Brønsted-Lowry base) is known to drive the reaction, the gas-phase reaction follows the "mobile proton model" to form the products via a number of intermediates, some the same as in their condensed-phase counterparts. Energy-resolved mass spectrometry, deuterium labeling experiments, and theoretical calculations (B3LYP/6-31G**) identified 27 different reaction routes in the gas phase, forming a complex interlinked reaction network. The experimental measurements and theoretical calculations confirm the proton hopping onto different basic sites of the precursors and intermediates to transform them ultimately into isoquinoline.

Synthesis of Isoquinolines from Benzimidates and Alkynes via Cobalt(III)-Catalyzed C-H Functionalization/Cyclization.

C-H alkenylation/annulation of benzimidates with alkynes has been realized by using a Cp*Co(III) catalyst under air. A series of substituted isoquinolines were obtained with moderate to good yields under mild reaction conditions.