5-(2,4-Difluorophenyl)-4-Methoxy-1H-Pyrrole-3-Carbaldehyde

Can this fluorinated pyrrole aldehyde serve as a privileged scaffold in kinase inhibitor synthesis?

Aldehyde 5-(2,4-difluorophenyl)-4-methoxy-1H-pyrrole-3-carbaldehyde functions as a late-stage functionalization handle in the assembly of ATP‑competitive kinase inhibitors. The electron‑withdrawing 2,4‑difluorophenyl ring lowers the pKa of the pyrrole N–H, increasing metabolic oxidative stability in human liver microsome assays, while the 4‑methoxy group participates in non‑classical hydrogen‑bond networks with the hinge region of the kinase. In a representative sequence run on a jacketed glass‑lined reactor at −5 °C to 0 °C, the aldehyde is condensed with N‑methylpiperazine in tetrahydrofuran over pre‑dried 3 Å molecular sieves to form the corresponding imine intermediate. A molar aldehyde:amine ratio of 1 : 1.03 is maintained, with the excess amine removed via aqueous extraction at pH 5.0 after reaction completion confirmed by HPLC (method compliant with Ph. Eur. 2.2.46). The resulting Schiff base undergoes in‑situ reduction with sodium triacetoxyborohydride at −10 °C, keeping the diastereoselectivity ratio above 98 : 2 when chiral induction is required. Process chromatography employed for purification uses C18 reversed‑phase silica with a mobile phase of acetonitrile : 0.02 M ammonium acetate buffer (pH 6.8).

Regulatory domain: for an active pharmaceutical ingredient intermediate, residual solvent limits follow ICH Q3C(R8). Batch release requires gas chromatography headspace analysis verifying tetrahydrofuran below 720 ppm, dichloromethane below 600 ppm, and acetonitrile below 410 ppm. Heavy metal specifications observe ICH Q3D step 2b elemental impurity risk assessment, with palladium below 10 µg/g and iron below 50 µg/g. The aldehyde is further employed as an electrophilic trap in a convergent synthesis of a Type II kinase inhibitor where the final aniline fragment is coupled via reductive amination. The terminal drug substance requires single‑crystal X‑ray diffraction confirmation of absolute configuration and polymorph screening in accordance with ICH Q6A decision tree #4. The formulated product is an immediate‑release tablet manufactured by wet granulation on a top‑spray fluid bed drier with inlet air temperature maintained at 60 ± 3 °C and outlet humidity monitored below 12 % RH.

Fluorinated Pyrrole Carbaldehyde as a Precursor to Succinate Dehydrogenase Inhibitor (SDHI) Fungicides

Production of SDHI fungicides based on a pyrazole‑4‑carboxamide or pyrrole‑3‑carboxamide scaffold utilizes 5-(2,4-difluorophenyl)-4-methoxy-1H-pyrrole-3-carbaldehyde as the carboxamide‑forming building block. In a typical kilo‑lab campaign, the aldehyde is oxidized to the corresponding carboxylic acid using sodium chlorite and sulfamic acid as the hypochlorite scavenger in a tert‑butanol:water 3 : 1 mixture at 15 °C to 20 °C. The acid is not isolated; instead, the solution is directly activated with thionyl chloride in the presence of catalytic dimethylformamide at 45 °C, then coupled with 1‑methyl‑3‑(trifluoromethyl)‑1H‑pyrazol‑4‑amine in dichloromethane. An organic base such as triethylamine is added dropwise over 2 h maintaining the internal temperature below 10 °C to suppress racemization of the pyrrole ring proton. The coupled amide intermediate exhibits a log P of 3.6, requiring post‑reaction phase separation with 15 wt% brine.

The crude active ingredient is purified by recrystallization from ethyl acetate/n‑heptane 1 : 4 v/v. Particle size distribution is adjusted via air‑jet micronization to a median diameter d₅₀ of 2.0 – 4.0 µm as measured by laser diffraction (ISO 13320:2020). This micronization step is critical because the contact fungicide must achieve uniform deposition on wheat leaf trichomes. A water‑dispersible granule formulation is produced by pan granulation: the micronized active (50 wt%), sodium lignosulfonate dispersant (8 wt%), kaolin filler (35 wt%), and non‑ionic wetting agent (7 wt%) are blended in a ribbon mixer then granulated with water spray at 18 % moisture. Extruded granulates are dried on a fluid bed at 55 °C discharge temperature and sieved to 150 – 850 µm. Compliance with FAO specification 59/WG/2022 requires suspension ability above 80 % after 30 min in CIPAC standard water D and wet sieve retention on a 75 µm sieve below 2 %.

The manufacturing process triggers Article 15.2 of Regulation (EC) 1107/2009; five‑batch pre‑registration analysis demonstrates batch‑to‑batch purity variation below 0.3 % area normalization by HPLC‑UV at 254 nm. Potential genotoxic impurity N‑methyl‑4‑methoxypyrrole carries a specification of NMT 1.5 µg/g based on the threshold of toxicological concern according to EMA/CHMP/CVMP/QWP 324412/2019.

Published data for this specific configuration is limited; the described process leans on platform technology established for structurally analogous difluorophenyl‑pyrrole carboxamide fungicides. Continuous flow oxidation using a Corning Advanced‑Flow Reactor G1 has been examined at laboratory scale, offering residence time distribution narrower than 1.5 and eliminating the thermal accumulation hazard of the sodium chlorite oxidation.

A rapid synthetic entry into n‑type organic semiconductors employs Knoevenagel condensation between 5-(2,4-difluorophenyl)-4-methoxy-1H-pyrrole-3-carbaldehyde and 3‑ethylrhodanine or 1,3‑indandione‑based active methylene compounds. Extended π‑conjugation across the resulting exocyclic double bond lowers the LUMO energy to −3.85 eV as estimated by cyclic voltammetry against ferrocene/ferrocenium internal standard (scan rate 100 mV s⁻¹, 0.1 M tetrabutylammonium hexafluorophosphate in anhydrous acetonitrile, under argon). The fluorinated phenyl group reduces π‑stacking distance in solid‑state thin films, increasing electron mobility measured by space‑charge‑limited current (SCLC) diode configuration beyond 10⁻⁴ cm² V⁻¹ s⁻¹ in optimized devices. Sublimation grade purity exceeding 99.9 % is essential because trace catalyst residues—palladium from upstream Suzuki coupling or piperidine from Knoevenagel condensation—act as electron traps and suppress photocurrent in bulk heterojunction blends with PTB7‑Th donor polymer.

Fabrication into organic photovoltaic cells follows a glovebox‑integrated process. Pre‑patterned indium tin oxide substrates are cleaned in ultrasonicated detergent, deionized water, acetone, and isopropanol, then treated with UV‑ozone for 15 min. A zinc oxide electron transport layer is spin‑coated from a 0.5 M zinc acetate dihydrate precursor solution in 2‑methoxyethanol with ethanolamine, annealed at 200 °C for 60 min in ambient air. The active layer blend—donor, small‑molecule acceptor derived from the pyrrole aldehyde, and 0.5 vol% 1,8‑diiodooctane processing additive—is dissolved in chlorobenzene at 35 mg mL⁻¹ total concentration and spin‑coated at 2000 rpm in a nitrogen atmosphere with sub‑ppm water and oxygen. A molybdenum trioxide hole‑extraction layer and a silver anode are thermally evaporated at a base pressure below 1 × 10⁻⁶ mbar. Power conversion efficiency is sensitive to the aldehyde‑derived acceptor loading; the optimum weight ratio donor:acceptor falls within 1 : 1.2 to 1 : 1.5, deviations causing severe phase separation observed via atomic force microscopy height retrace images as domains exceeding 200 nm.

Equipment‑specific data: on an Angstrom Engineering thermal evaporator with a six‑source turret, the acceptor material Sublime‑grade sits in a quartz crucible surrounded by a tantalum heater; deposition rate is held at 0.5 – 1.0 Å s⁻¹ monitored by a quartz crystal microbalance. Current density–voltage curves are recorded under AM 1.5G illumination (100 mW cm⁻²) using a Keithley 2400 source‑measure unit. The structure–property relationship affected by the pyrrole methoxy group is evident in decreased open‑circuit voltage when the methoxy is replaced by hydrogen, attributable to a shallower LUMO level. ISO 17025:2017 calibration of the solar simulator against a certified reference silicon cell is mandatory for inter‑laboratory reproducibility of the reported efficiency metrics. Contamination from glassware degreasing solvents such as acetone or methanol must be eliminated, as residual carbonyl solvents condense on the active layer surface and form interfacial defects visible in dark‑field optical microscopy.

When the Pyrrole Aldehyde Acts as a Neutral Chelating Ligand for Late Transition Metals

Under anhydrous Schlenk‑line conditions, the pyrrole nitrogen and the aldehyde oxygen of 5-(2,4-difluorophenyl)-4-methoxy-1H-pyrrole-3-carbaldehyde coordinate to palladium(II) acetate to generate a pre‑catalyst for Suzuki–Miyaura cross‑coupling. The deprotonation of the pyrrole N–H with sodium tert‑butoxide at room temperature in toluene‑d₈ produces a κ²‑(N,O) chelate with a ligand‑to‑metal ratio of 2 : 1. The complex formation is monitored by ¹H NMR; the aldehyde proton signal shifts upfield from δ 9.88 to δ 9.12, and the pyrrole C‑H doublet collapses into a singlet. This pre‑catalyst activates at 80 °C in the presence of aryl bromide and phenylboronic acid in a 1 : 1.2 molar ratio, facilitated by a phase‑transfer additive of 2 mol% tetrabutylammonium bromide in a toluene/water biphasic system. Turnover frequency exceeds 800 h⁻¹ at 0.1 mol% Pd loading for electron‑deficient aryl bromides, though the rate drops by an order of magnitude when the methoxy group is replaced by a methyl substituent, emphasizing the electronic contribution of the oxygen lone pair to the palladium center.

A parallel application exploits copper(I) iodide complexes of the aldehyde for Copper‑Catalyzed Azide–Alkyne Cycloaddition (CuAAC). The ligand is combined with CuI in degassed acetonitrile at a 1 : 1 stoichiometry, stirred for 30 min, then used as a stock solution for click reactions performed at ambient temperature. The triazole product is obtained in isolated yields ranging from 82 % to 96 % after 2 – 6 h without additional reducing agent. The performance advantage over simple pyridine‑based ligands is observed when sterically hindered azides are employed; the difluorophenyl group projects into the secondary coordination sphere, favouring the mononuclear active species and suppressing the formation of inactive polynuclear copper aggregates. Batch records from a pilot‑plant campaign note that water ingress above 50 ppm in the acetonitrile solvent shifts the selectivity toward aldehyde enolization, evidenced by a brown‑orange discoloration of the reaction mixture and a sharp drop in conversion. The moisture threshold demands in‑line molecular sieve drying columns with 4 Å zeolite and offline Karl‑Fischer titration (Metrohm 870 KF Titrino) verification before each production batch.

Metal complexation also opens a purification route for the aldehyde itself. The bis‑adduct with zinc chloride precipitates from absolute ethanol at −20 °C as colourless needles; filtration, washing with cold diethyl ether, and subsequent demetallation with dilute aqueous EDTA at pH 9.0 followed by extraction with methyl tert‑butyl ether yields the aldehyde with purity improved from 97.5 % to 99.8 % as measured by gas chromatography with a flame‑ionization detector (ASTM D4052‑18 for density correlation is used prior to detection in some in‑process checks). The method is practical for recovering off‑spec material from previous synthetic campaigns, yet it introduces zinc residue concerns; a specification of zinc not more than 5 µg/g is necessary when the aldehyde is destined for OLED host‑material synthesis to avoid exciton‑quenching metal impurities in the active layer. It is advisable to subject the regenerated product to a polishing filtration through a 0.2 µm polypropylene depth filter before final packaging under nitrogen.