Methyl 6H-Thieno[2,3-B]Pyrrole-5-Carboxylate

Methyl 6H-Thieno[2,3-B]Pyrrole-5-Carboxylate introduced as a bifunctional monomer for donor–acceptor copolymers is first converted to its 2,6-dibromo derivative via N-bromosuccinimide-mediated halogenation in anhydrous DMF at 0–5 °C under argon. The crude dibromide is purified by gradient sublimation at 10⁻³ mbar and 145 °C until residual succinimide content falls below 0.1 % by HPLC‑UV, meeting the electronic‑grade specification of ≤ 10 ppb total metals as verified by ICP‑MS per SEMI C41-0618. Stille polycondensation with 2,5‑bis(trimethylstannyl)thieno[3,2‑b]thiophene is conducted in a Braun MBraun LABstar glovebox (H₂O, O₂ 0.1 ppm) using anhydrous chlorobenzene, Pd₂(dba)₃ at 0.02 equiv, and tri(o‑tolyl)phosphine at 0.08 equiv. The reaction mixture is heated in a Biotage Initiator+ microwave synthesizer at 140 °C for 45 minutes with simultaneous power modulation to maintain a pressure ceiling of 3 bar. The resulting poly(thienopyrrole‑alt‑thienothiophene) is end‑capped with 2‑bromothiophene and precipitated into methanol, followed by Soxhlet extraction with acetone, hexane, and chloroform to remove oligomers below Mₙ 15 kDa. Gel permeation chromatography against polystyrene standards in 1,2,4‑trichlorobenzene at 150 °C returns a target molecular weight of Mₙ 28–35 kDa with a dispersity ≤ 1.8. Solution‑processed films are blade‑coated on octadecyltrichlorosilane‑treated SiO₂/Si substrates at a wet thickness of 80 µm and annealed for 10 min at 180 °C on a hot plate with a surface temperature uniformity of ± 2 °C. Bottom‑gate top‑contact organic field‑effect transistors exhibit hole mobilities of 0.4–0.6 cm²/V·s as derived from the saturation regime transfer curve measured with a Keithley 4200‑SCS parameter analyzer under nitrogen, in accordance with the test structures described in IEEE 1620‑2008. The threshold voltage shifts by less than 0.8 V after 10⁴ s continuous bias stress when the active channel is encapsulated with a parylene‑C layer deposited at 25 nm/min via a Specialty Coating Systems PDS 2010. Pre‑drying of the methyl ester monomer at 40 °C for 48 h in a vacuum oven is mandatory if relative humidity during storage has exceeded 40 %; failure to do so results in ester hydrolysis during bromination, yielding a mono‑acid by‑product that acts as a chain‑transfer agent and reduces molecular weight below the entanglement threshold of ~19 kDa, leaving the film brittle and unsuitable for flexible substrates. The derived electron‑acceptor copolymer blended with ITIC‑4F in a 1:1.2 weight ratio with 0.5 vol% 1,8‑diiodooctane achieves a power conversion efficiency of 9.2 % under AM 1.5G illumination at 100 mW/cm² when the active layer thickness is held between 95 and 110 nm, though published data for this exact ester‑based acceptor unit remain limited and device performance is acutely sensitive to batch‑to‑batch variation in the monomer’s tin content.

What Limits Reaction Yield During the Final Suzuki Coupling of the Boronic Ester Derivative in cGMP Intermediates?

During the synthesis of a proprietary kinase inhibitor candidate, the carboxylate ester is advanced to its pinacol boronic ester by palladium‑catalyzed borylation with bis(pinacolato)diboron in the presence of potassium acetate and Pd(dppf)Cl₂·CH₂Cl₂ (0.03 equiv) in 1,4‑dioxane at 100 °C. The boronate intermediate is telescoped without isolation into an aqueous Suzuki coupling with a 2‑chloro‑5‑trifluoromethylpyridine partner under phase‑transfer conditions using tetra‑n‑butylammonium bromide (0.15 equiv) and aqueous potassium carbonate (2 M). The intrinsic yield ceiling of this telescoped process—typically 72–78 %—is traced to competitive protodeboronation that accelerates above pH 10.5 and when the internal temperature momentarily exceeds 85 °C. Consequently, the reactor train is configured with two linked 50 L Hastelloy C‑276 vessels: the first dedicated to borylation under 0.3 bar positive nitrogen, the second receiving the filtered boronate solution and dosed with the heteroaryl chloride at a controlled rate of 0.8 mol/h while maintaining a jacket temperature setpoint of 78 °C with cascade PID tuning that restricts overshoot to ± 0.5 °C. Compliance with ICH Q7 for GMP starting materials is demonstrated by a vendor qualification package that includes residual palladium below 10 ppm by USP <233> (ICP‑MS), inorganic arsenic below 1.5 ppm per USP <223>, and a nitrosamine risk evaluation following the EMA Q&A method with a threshold of toxicological concern of 1.5 µg/day. The methyl ester itself appears as a chromatographic purity marker on the in‑process control monograph; acceptance criterion is a single peak ≥ 99.0 area% by HPLC (C18, 254 nm). In the final two chemical steps the ester is hydrolyzed with lithium hydroxide in THF/water (3:1) and coupled to (S)‑3‑aminopiperidine dihydrochloride using HATU (1.15 equiv) and DIPEA (3.5 equiv) in DMF. The isolation of the API hydrochloride monohydrate is achieved by pH‑swing crystallization from isopropanol, yielding a polymorphic Form A with a melting onset of 228 °C by DSC (DIN EN ISO 11357‑1). Terminal dosage forms are immediate‑release tablets containing 25 mg or 80 mg of the active ingredient. The ester’s supply chain must document absence of dimethyl sulfate or alkylating agent carry‑over because the downstream amine displays a genotoxic alert for N‑alkylation; the vendor’s statement of compliance references REACH Annex XVII entry 28. Once the ester is received, storage at 2–8 °C under argon with a desiccant cartridge is mandatory: exposure to ambient moisture for more than 8 h leads to clumping and a drop in assay by 1.2 % per 24 h due to incipient hydrolysis.

Insecticidal Isoxazoline Precursors and the Supply of 5‑Carboxylate Thienopyrrole Intermediates

A contact insecticide active against Hemiptera and Thysanoptera is elaborated by transforming Methyl 6H-Thieno[2,3‑B]Pyrrole‑5-Carboxylate into the corresponding N‑chloroacetyl derivative, which is subsequently condensed with 2,6‑difluorobenzonitrile oxide generated in situ from the corresponding oxime chloride and triethylamine in diethyl ether at −10 °C. The 1,3‑dipolar cycloaddition produces the isoxazoline pharmacophore with a regioselectivity exceeding 92 % when the chloride precursor’s purity is kept above 98.5 %. The technical material is formulated as a 120 g/L suspension concentrate; the pre‑milling composition contains the active ingredient at 11.2 wt%, ethoxylated tristyrylphenol phosphate (2.5 wt%), a naphthalene sulfonate condensate dispersant (3.8 wt%), propylene glycol (5.0 wt%), and a silicone antifoam (0.2 wt%). Wet milling is performed on a Netzsch MiniCer mill charged with 0.3 mm yttria‑stabilized zirconia beads at a throughput of 80 kg/h until the particle size distribution yields a D₉₀ 3.5 µm as verified by laser diffraction (ISO 13320:2020). Pesticide specification compliance is benchmarked against the FAO Manual on the Development and Use of FAO Specifications for Plant Protection Products, section 9.2.6 for suspension concentrates, requiring a suspensibility of ≥ 85 % after 30 min in CIPAC Standard Water D and a wet sieve retention on a 75 µm mesh ≤ 0.1 %. The hydrolysis half‑life of the active ingredient at 54 °C (accelerated storage per CIPAC MT 46.3) must not decrease by more than 5 % absolute over 14 days. Incompatibility is noted with copper‑based co‑formulants: chelation between the isoxazoline nitrogen and Cu(II) reduces biological efficacy by 30–40 % in tank‑mix trials on cotton aphid (Aphis gossypii). The terminal product is packaged in 1 L fluorinated HDPE bottles and applied as a foliar spray at a rate of 75–100 mL/hL water, which delivers a field dose of 90–120 g a.i./ha. Ecotoxicological data packages, required for OECD dossier submission, include an acute contact test on adult honeybees (OECD 214) with an LD₅₀ > 100 µg/bee.

Polyester dyeing operations utilising a blue disperse dye whose heterocyclic building block originates from Methyl 6H‑Thieno[2,3‑B]Pyrrole‑5‑Carboxylate begin with the preparation of the free amine via Curtius rearrangement of the corresponding hydrazide formed by ester hydrazinolysis. The resulting 5‑aminothienopyrrole is diazotized with nitrosylsulfuric acid in a sulfuric acid‑phosphoric acid mixture at −5 °C and immediately coupled with a N‑cyanoethyl‑N‑benzyl‑m‑toluidine component, which has been pre‑dissolved in a pH 2.5–3.0 buffer containing acetic acid and sulfamic acid. The presscake is washed to a conductivity 50 µS/cm and oven‑dried under vacuum at 70 °C to a moisture content of 0.3 %. Standardisation to a color strength of 200 % relative to a type product is achieved by blending with sodium lignosulfonate (35 wt%) and a condensate dispersant (15 wt%) followed by micronisation in a horizontal bead mill (WAB Dyno‑Mill KD‑20) until the filter test value measured according to the “Vat filter test” drops below 200 mbar. The finished powder is incorporated into a dye bath at concentrations of 0.5–2.5 % owf together with a levelling agent (1.0 g/L) and acetic acid (0.5 mL/L) at pH 4.5; dyeing is conducted in a Mathis Labomat IR with a heating rate of 2 °C/min to 130 °C, held 45 min, followed by an alkaline reduction clearing with sodium dithionite (2.0 g/L) and caustic soda (4.0 mL/L) at 80 °C for 20 min. Color fastness to washing (ISO 105‑C06, A1S, 60 °C) returns a staining rating of grade 4–5 on polyamide and acetate, while wet rubbing fastness (ISO 105‑X12) attains grade 4 on a standard cotton rubbing cloth. The dye’s registration dossier under the ZDHC Manufacturing Restricted Substances List is maintained with an updated analytical confirmation that no arylamines listed under REACH Annex XVII, Entry 43 are generated during the dyeing process nor upon reductive cleavage of the final garment. Warehousing of the carboxylate ester upstream must avoid proximity to sodium hydroxide flake storage, as ambient alkaline dust causes surface degradation that lowers the amine yield by 2–4 % per week of exposure.

When Anhydrous Hydrolysis of the Methyl Ester Prerequisites the Assembly of a Copper(II) Paddlewheel Metal–Organic Framework

Conversion of Methyl 6H‑Thieno[2,3‑B]Pyrrole‑5‑Carboxylate to the free carboxylic acid ligand is carried out in a 20 L glass‑lined reactor under a constant nitrogen sweep. The ester (2.0 kg, 11.0 mol) is dissolved in degassed THF (12 L) and treated with a LiOH·H₂O solution (1.1 equiv in 3 L water) that is pre‑sparged with argon for 60 min. Full saponification monitored by TLC (hexane:ethyl acetate 1:1) is reached after 6 h at 25 °C. The pH is adjusted to 2.0 with 2 M HCl while maintaining a jacket temperature of 10 °C; the precipitated acid is filtered, washed with cold de‑ionized water until the filtrate chloride concentration drops below 5 ppm, and vacuum‑dried at 50 °C to a loss on drying of 0.1 %. The resulting 6H‑thieno[2,3‑b]pyrrole‑5‑carboxylic acid displays a decomposition temperature of 215 °C by thermogravimetric analysis (ASTM E1131‑20) and must be stored over phosphorus pentoxide in a desiccator—failure to do so results in a 1.8 % mass uptake over 48 h under ambient laboratory conditions, causing hydrate formation that impedes framework crystallisation. Solvothermal synthesis of the copper paddlewheel MOF is performed by dissolving Cu(NO₃)₂·2.5H₂O (2.0 mmol) and the acid ligand (1.0 mmol) in a 15 mL mixture of DMF, ethanol, and deionized water (3:1:1 v/v/v) with 100 µL concentrated HNO₃ as modulator. The solution is sealed in a 23 mL PTFE‑lined Parr acid digestion vessel and placed in a pre‑heated forced‑convection oven at 85 °C for 72 h. Octahedral blue crystals are harvested by filtration, washed with DMF and methanol, and subjected to supercritical CO₂ activation using a Separex SFE‑200 at 100 bar and 40 °C for 4 h to prevent pore collapse. The BET surface area determined by nitrogen adsorption at 77 K according to ISO 9277:2010 is 1,420 m²/g with a total pore volume of 0.68 cm³/g at p/p₀ = 0.95. A mixed‑matrix membrane for post‑combustion CO₂ capture is fabricated by dispersing the activated MOF at 15 wt% in a Matrimid 5218 polyimide dope solution dissolved in NMP, casting with a doctor blade set to 400 µm gap on a glass plate, and phase‑inverting in a water bath at 22 °C. Single‑gas permeation measurements at 3 bar and 35 °C yield a CO₂ permeability of 23 barrer and a CO₂/N₂ ideal selectivity of 44. The operational boundary of the regenerated acid is its irreversible oligomerization when heated neat above 180 °C in the absence of solvent, forming anhydride‑linked chains that are no longer competent for MOF assembly.