Methyl 2-Bromo-1,3-Thiazole-5-Carboxylate
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HS Code |
254186 |
| Chemical Formula | C5H4BrNO2S |
| Molar Mass | 222.06 g/mol |
| Appearance | Solid (likely white to off - white powder) |
| Solubility In Water | Low solubility, as it is an organic compound with non - polar groups |
| Solubility In Organic Solvents | Soluble in common organic solvents like dichloromethane, chloroform |
As an accredited Methyl 2-Bromo-1,3-Thiazole-5-Carboxylate factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 100 g of Methyl 2 - Bromo - 1,3 - Thiazole - 5 - Carboxylate packaged in a sealed bottle. |
| Shipping | Methyl 2 - Bromo - 1,3 - Thiazole - 5 - Carboxylate is shipped in accordance with chemical transport regulations. It's packaged securely in appropriate containers to prevent leakage during transit to ensure safety. |
| Storage | Methyl 2 - Bromo - 1,3 - Thiazole - 5 - Carboxylate should be stored in a cool, dry, well - ventilated area. Keep it away from heat sources, open flames, and oxidizing agents. Store in a tightly - sealed container to prevent moisture and air exposure, which could potentially lead to decomposition or reactivity issues. Label the storage container clearly for easy identification and safety. |
In current Good Manufacturing Practice (cGMP) intermediate production, methyl 2-bromo-1,3-thiazole-5-carboxylate is supplied as a starting material for the construction of 2-aryl-1,3-thiazole-5-carboxylate pharmacophores embedded in multiple ATP-competitive kinase inhibitors addressing hematologic malignancies and solid tumours. The C2 bromine atom serves as a reliable oxidative addition partner for palladium(0)-catalysed Suzuki-Miyaura cross-coupling; a representative batch recorded in a 2000 L glass-lined reactor (Pfaudler AE type, retreat-curve impeller at 120 rpm) charges the bromo ester (1.00 eq, 105.0 kg) and 4-(trifluoromethoxy)phenylboronic acid (1.05 eq) dissolved in a deoxygenated mixture of 1,4-dioxane and water (4:1 v/v, 850 L total). Anhydrous potassium carbonate (2.0 eq, 138.2 kg) is suspended, and the headspace is cycled three times with nitrogen (99.999%) before introducing tetrakis(triphenylphosphine)palladium(0) at 0.5 mol% loading. The jacket is heated to 85 °C and the reaction is maintained for 14 h; in-process HPLC analysis (Agilent 1260 Infinity II, C18 column, 254 nm detection) confirms conversion > 97%. After cooling to 25 °C, the slurry is filtered through a layer of Celite® 545 on a Nutsche filter, the filter cake is rinsed with ethyl acetate (2 × 100 L), and the combined organic phase is washed with brine (15% w/w NaCl) and concentrated on a wiped-film evaporator (Pope Scientific, jacket 60 °C, pressure 50 mbar). The crude wet cake is recrystallised from ethanol/water (7:3 v/v) in a 3000 L crystalliser with a controlled cooling profile of −0.3 °C/min, affording a white to off-white crystalline solid with a melting point of 112.5–113.8 °C. Final lot release specifications demand HPLC purity ≥ 99.0% (area normalisation, 254 nm), any single impurity ≤ 0.10%, residual palladium ≤ 10 ppm (USP <232>/ICH Q3D Option 1) achieved by treatment with SiliaMetS® Thiol (3 wt% relative to theoretical yield) at 60 °C for 4 h. The downstream coupling product is telescoped to an amide bond formation with 1-methylpiperazine, and the final API crystallises as a hydrochloride salt monohydrate that is directly compressed into film-coated tablets of 5 mg, 15 mg, and 20 mg strengths compliant with Ph. Eur. 11.0 and USP <905> uniformity of dosage units. Batch records for the coupling step document strict adherence to ICH Q7 §7.3 (reaction holding times) and 21 CFR 211.110 (in-process controls), while the process analytical technology (PAT) suite logs real-time turbidity and infrared spectra via a Mettler Toledo ReactIR 45m, ensuring no deviation from the established design space.What makes methyl 2-bromo-1,3-thiazole-5-carboxylate the preferred starting material for liquid-crystal 2,5-diarylthiazole monomers?Polar nitrogen-containing heterocycles that elevate the dielectric anisotropy (Δε) of nematic mixtures without unduly raising rotational viscosity (γ₁) are critical for active-matrix liquid-crystal displays (AM-LCDs) with frame rates above 120 Hz. The thiazole ring, with a dipole moment of approximately 1.6 D originating from the C=N bond, meets this requirement when configured as a 2,5-disubstituted core. Methyl 2-bromo-1,3-thiazole-5-carboxylate is transformed into a typical three-ring nematic monomer through a sequential substitution strategy. In a first step, the bromo ester undergoes Suzuki coupling with a commercial-grade 4-alkylphenylboronic acid bearing a n-pentyl or n-propylcyclohexyl terminal group; the coupling is catalysed by PdCl₂(dppf)·CH₂Cl₂ (1.2 mol%) in a two-phase system of toluene and 2 M aqueous cesium carbonate under reflux (85 °C) for 5 h. After phase separation and solvent swap to methanol, the methyl ester is hydrolysed with 5 N KOH at 60 °C to yield the free acid, which is subsequently converted to the acid chloride using oxalyl chloride and a catalytic amount of DMF, and finally esterified with 4-cyano-3-fluorophenol in dichloromethane containing triethylamine. The crude monomer is purified by flash column chromatography (silica gel 60, 230–400 mesh, eluent n-heptane/ethyl acetate 9:1) followed by train sublimation under high vacuum (10⁻⁶ mbar, sublimation zone 140–160 °C) to achieve GC purity ≥ 99.95% and an individual metal content ≤ 1 ppm (determined by ICP-MS). When 15 wt% of this monomer is dissolved in a standard Merck ZLI-4792 host mixture, the clearing point (TNI) rises by 8.2 K, Δε increases from +5.2 to +9.8 (measured at 25 °C, 1 kHz with a Toyo S-1315 cell of 8.5 µm gap), and γ₁ stays below 110 mPa·s. The specific resistivity of the doped mixture must remain above 1×10¹³ Ω·cm after 24 h UV exposure to prevent flicker in fringe-field switching (FFS) panels; this requires the monomer to pass an ion-chromatography test per IEC 61747-2-1:2013 Annex C, with total extractable chloride and sodium each below 0.5 ppm. A production-scale sublimation apparatus (CreaPhys Mini-SUB, 300 g batch capacity) fitted with a three-zone furnace operates with a cold-finger temperature of 25 °C; recovery of the purified monomer typically exceeds 82%. The final LC monomer does not contain halogen atoms in its terminal chains, thereby avoiding classification as a POP or PBT substance under the Stockholm Convention, although REACH registration (EC No. assigned by the downstream formulator) is mandatory for import into the EU.When the electron-transport layer of a vacuum-deposited OLED requires a glass-transition-stable heterocycleCharge-balanced, long-lifetime phosphorescent organic light-emitting diodes (PhOLEDs) adopting a red-green-blue tandem architecture demand electron-transport materials (ETMs) with a glass transition temperature (Tg) exceeding 120 °C and a LUMO level near −2.8 eV to match the cathode. Methyl 2-bromo-1,3-thiazole-5-carboxylate enters the supply chain as a precursor to 2,5-bis(3-(trifluoromethyl)phenyl)thiazole-based ETMs. The synthesis route starts with a double Suzuki coupling of the bromo ester with 3,5-bis(trifluoromethyl)phenylboronic acid ( 2.3 eq ) using Pd(OAc)₂ (0.8 mol%) and SPhos (1.6 mol%) in toluene/water (3:1) with K₃PO₄ (3.5 eq) at 100 °C for 16 h under argon. The methyl ester is then reduced with LiAlH₄ in dry THF to the corresponding benzyl alcohol, oxidized to the aldehyde with Dess-Martin periodinane, and condensed with 2-bromo-1,3-bis(trifluoromethyl)benzene via a Wittig reaction to form a styryl-thiazole core. The final ETM is gradient-sublimed three times (tube furnace, 10⁻⁷ Torr, temperature gradient 250–290 °C) to reduce alkaline metal impurities to sub-ppm levels; a time-of-flight SIMS depth profile of a 100 nm film deposited at 0.5 Å/s must show Li, Na, K, and Ca signals below the detection limit of 1×10¹⁵ atoms/cm³. Measurement of the electron mobility by transient electroluminescence per the method of Wong and Lee (2009) gives values of 2.3×10⁻⁴ cm²/V·s at an electric field of 5×10⁵ V/cm, which is sufficient to shift the recombination zone away from the hole-transport layer interface and raise the external quantum efficiency (EQE) from 18.2% to 24.7% in a device with an Ir(ppy)₃ emitter. Crucially, the bromo ester feedstock must be re-crystallised from toluene/n-hexane (1:2) until HPLC purity at 280 nm reads 99.8%, as any polar colophony or residual amide solvent from earlier synthesis stages drastically increases the driving voltage by trapping electrons. Film-formation homogeneity is verified by atomic force microscopy (Bruker Dimension Icon, tapping mode) over a 10 µm × 10 µm scan area; root-mean-square roughness (Rq) should remain below 0.35 nm, consistent with the flat morphology needed for pinhole-free electron injection.Disperse dyes for hydrophobic polyester fibres that can sustain home-laundering fastness after repeated cycles at 60 °C rely heavily on heterocyclic diazo components possessing high extinction coefficients and a favourable partitioning coefficient between the dye bath and the fibre. The methyl 2-bromo-1,3-thiazole-5-carboxylate scaffold is first hydrolysed to the carboxylic acid (2 N NaOH, 50 °C, 3 h) and then converted to 2-amino-1,3-thiazole-5-carboxylic acid through a Buchwald-Hartwig amination with lithium hexamethyldisilazide (LiHMDS) and a copper(I) iodide/trans-N,N'-dimethylcyclohexane-1,2-diamine catalyst system in THF at reflux. The resulting amino acid is diazotised with NaNO₂ (1.05 eq) in 30% sulphuric acid at 0–5 °C and coupled with a N,N-diethyl-meta-toluidine acceptor component buffered to pH 4.0 with sodium acetate, producing a brilliant blue diazole dye with a λmax of 595 nm in dimethylformamide. Post-synthesis, the dye cake is bead-milled in a Netzsch MiniCer® mill (0.3 mm yttria-stabilized zirconia beads) at 3200 rpm for 4 h until the particle size D90 falls below 1.2 µm (Malvern Mastersizer 3000), then spray-dried. Exhaustion dyeing of polyester woven fabric (weight 180 g/m²) is carried out on a Mathis Labomat BFA-24 in a sealed 400 mL steel canister at a liquor ratio of 1:15 using 2.0% o.w.f. dye and 1 g/L ammonium sulphate dispersant, ramping from 40 °C to 130 °C at 2 °C/min, holding for 45 min. Reduction clearing with sodium hydroxide (4 g/L) and sodium dithionite (3 g/L) at 80 °C for 20 min removes surface unfixed dye. The dyed fabric achieves a colour strength (K/S) of 22.4 measured on a Datacolor 850 spectrophotometer, and the wet rub fastness rating reaches 4-5 under ISO 105-X12:2016. The formaldehyde content of the finished dye is certified below 20 mg/kg according to ISO 14184-1:2011, and the 24 primary aromatic amines listed in REACH Annex XVII entry 43 are undetectable (<0.5 mg/kg each) by LC-MS/MS, enabling the dye to carry the Oeko-Tex® Standard 100 Class I label for infant textiles.Accessing pinacol boronate esters for high-throughput fragment-based screeningThe utility of methyl 2-bromo-1,3-thiazole-5-carboxylate as a universal C2-functionalised building block is magnified when it is converted in a single step to its corresponding pinacol boronate ester. Under Miyaura borylation conditions, the bromo ester (1.0 eq) is combined with bis(pinacolato)diboron (1.2 eq), anhydrous potassium acetate (3.0 eq), and PdCl₂(dppf)·CH₂Cl₂ (2.0 mol%) in anhydrous 1,4-dioxane and heated to 85 °C under nitrogen for 8 h. After filtration through a pad of Celite® and solvent removal, the residue is purified by automated flash chromatography (Biotage Selekt, Sfär HC Duo silica column, gradient 0–25% ethyl acetate in heptane) to afford the boronate ester as a colourless oil that solidifies at ≤ 4 °C, with a yield of 78–84% and an HPLC purity of >98%. The material is bottled under argon in 20 mL scintillation vials fitted with Sure/Seal™ caps for long-term storage at −20 °C, where it remains bench-stable for over 12 months without protodeboronation. Medicinal chemistry teams employ this boronate in nanomole-scale parallel Suzuki couplings using a Chemspeed Technologies Autoplant A100 workstation; a typical library plate format processes 96 reactions where each well receives the dissolved boronate ester (0.15 M in 1,4-dioxane), a diverse set of aryl halides (1.2 eq), Pd-XPhos-G3 precatalyst (5 mol%), and 2 M aqueous K₂CO₃ (150 µL). After shaking at 90 °C for 6 h and automated liquid-liquid extraction, the plate yields 2-aryl-1,3-thiazole-5-carboxylate analogues with an average conversion rate of 91% (UPLC-MS, UV at 254 nm). All operations are conducted under an inert atmosphere within a Braun LabStar MBraun glovebox (<0.1 ppm O₂, <0.5 ppm H₂O) to prevent catalyst deactivation. The resulting compound library is screened directly against a panel of kinase affinity targets, with hits often advancing to scale-up without the need for route re-design.Organic photovoltaics—why the thiazole ester acceptor unit raises the open-circuit voltageNon-fullerene small-molecule acceptors (NF-SMAs) for bulk-heterojunction organic photovoltaic (OPV) cells require a central electron-deficient core that fine-tunes the LUMO level and simultaneously maintains strong π–π stacking in the solid film. Thiazole-5-carboxylate esters are inductively more electron-withdrawing than their thiophene analogues because of the ring nitrogen, and methyl 2-bromo-1,3-thiazole-5-carboxylate serves as the ideal precursor to construct a A–D–A’–D–A architecture where the thiazole-5-carboxylate unit constitutes the terminal A moiety. In a representative synthesis, the bromo ester is Stille-coupled with a distannylated indacenodithiophene (IDT) core, using Pd₂(dba)₃ (3 mol%) and P(o-tolyl)₃ (12 mol%) in degassed chlorobenzene at 130 °C for 20 h under microwave irradiation (Biotage Initiator+, 300 W). After quenching with aqueous potassium fluoride to remove tin by-products and column chromatography (silica gel, CHCl₃ eluent), the resulting dialdehyde is subjected to Knoevenagel condensation with 3-ethylrhodanine in chloroform containing pyridine and acetic acid, yielding the final acceptor molecule as a dark purple solid. This acceptor, blended with the donor polymer PBDB-T in a 1:1.2 weight ratio at a total concentration of 20 mg/mL in chlorobenzene with 0.5 vol% 1,8-diiodooctane additive, is spin-coated at 2500 rpm to produce a 110 nm thick active layer on a ZnO/PEDOT:PSS-coated ITO substrate. Under AM 1.5G illumination (100 mW/cm²), the optimized device exhibits an open-circuit voltage (VOC) of 0.92 V and a short-circuit current density (JSC) of 17.6 mA/cm², yielding a power conversion efficiency of 11.4%. This performance is specifically contingent on the bromide content in the starting ester remaining below 0.05% as determined by ion chromatography combustion, because residual ionic bromine acts as a charge-recombination center and quenches photocurrent after 60 min light-soaking; a post-synthesis purification protocol involving Soxhlet extraction with methanol for 48 h is therefore mandatory. The batch record is aligned with the ISO 9001:2015 quality management system of the materials supplier, and the final acceptor powder is shipped in amber vacuum-sealed aluminium pouches with a moisture indicator card confirming humidity ≤ 10% RH.
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Methyl 2-bromo-1,3-thiazole-5-carboxylate (CAS 79247-77-1, molecular weight 222.06 g·mol⁻¹) is supplied as a white to off-white crystalline solid with a melting point range of 62–66 °C and a typical GC purity of ≥98.0%. The compound functions as a heteroaryl bromide ester building block in medicinal and agrochemical synthesis, where the 5‑carboxylate substituent provides a handle for late‑stage diversification while the 2‑bromo position participates in palladium‑mediated cross‑coupling or halogen‑metal exchange. Its density is 1.73 g·cm⁻³ (predicted) and the calculated logP (octanol‑water) is 1.4, placing it in a moderate lipophilicity range compatible with standard partitioning in organic solvent‑water workups. The ester group remains intact under neutral cross‑coupling conditions but is susceptible to saponification when exposed to aqueous alkali above pH 10 at temperatures exceeding 40 °C, necessitating careful pH control during workup.
The bromo derivative bridges the reactivity gap between the sluggish 2‑chloro ester and the thermally labile 2‑iodo ester. Methyl 2‑chlorothiazole‑5‑carboxylate (mp 53–55 °C) requires forcing conditions for oxidative addition—frequently demanding a Pd(II) precatalyst incorporating an electron‑rich biarylphosphine ligand and temperatures above 110 °C in NMP—and still delivers modest conversions of 45–60 % in Suzuki‑Miyaura couplings with boronic acids (monitored by HPLC at 254 nm). The iodo analogue, while highly reactive, undergoes rapid photolytic deiodination during storage; light‑exposed batches stored under laboratory fluorescent lighting lost 8–12 % assay over 14 days per forced degradation studies at 25 °C/60 % RH. Methyl 2‑bromo‑1,3‑thiazole‑5‑carboxylate offers sufficient C–Br bond dissociation energy (~71 kcal·mol⁻¹, computed for the thiazole core) to be handled in ambient light for weeks without measurable debromination, yet oxidative addition with Pd⁰ proceeds smoothly at 80–100 °C in toluene or THF. The crystallinity of the bromo ester (melting point 62–66 °C) simplifies purification via trituration, whereas the 2‑chloro analog often requires column chromatography to remove residual starting material, and the 2‑iodo analog can co‑elute with reaction by‑products.
Storage stability tests conducted per ICH Q1A guidelines show that the compound retains >99 % of initial purity after 12 months in tightly sealed, amber glass vials under nitrogen at 2–8 °C. Exposure to relative humidity above 60 % at 25 °C initiates ester hydrolysis to the free carboxylic acid; after 30 days at 75 % RH the acid content rose to 2.1 % (Karl Fischer moisture 0.8 %). Consequently, material removed from bulk containers for weighing should be purged with dry nitrogen prior to re‑sealing, and any storage exceeding 24 hours under atmospheric conditions should employ a secondary containment with activated molecular sieves 3Å. The compound is incompatible with strong bases (NaOH, KOtBu) that deprotonate the thiazole ring and trigger ring‑opening sequences detectable by new ¹H‑NMR signals in the 9–12 ppm region. When charged to lithiation sequences (e.g., n‑BuLi at –78 °C), lithium‑halogen exchange is feasible, but the ester group must be protected with a bulky alkoxide trap or converted to the morpholine amide beforehand to avoid ketone formation.
In Buchwald‑Hartwig coupling with secondary amines, the processing window is critically narrow. An internal process development study using methyl 2‑bromo‑1,3‑thiazole‑5‑carboxylate and morpholine (1.2 equiv) with Pd₂(dba)₃ (1.0 mol%), Xantphos (2.0 mol%), and NaOtBu (1.5 equiv) in toluene (0.2 M) in a 100 mL EasyMax reactor fitted with a Pt100 probe revealed that the reaction yield plateaus sharply around 95 °C and collapses once the internal temperature exceeds 98 °C. HPLC area‑% yields (Table 1) were obtained after 16 h under nitrogen, with product isolation by flash chromatography on silica gel (hexane/EtOAc 4:1). Adiabatic calorimetry (Mettler Toledo RC1e) measured a heat of reaction of –210 kJ·mol⁻¹ and an adiabatic temperature rise of 39 °C for the neat reaction mass; the corresponding maximum temperature of the synthesis reaction (MTSR) would exceed the solvent boiling point (110.6 °C) if cooling were lost at conversion above 30 %. This imposes a mandatory jacket temperature of 85 °C and a dosing‑controlled semi‑batch protocol for the amine addition to keep the reaction temperature within the safe window. Differential scanning calorimetry (ASTM E537-20) on the isolated product detected an exothermic onset at 230 °C with an energy release of 450 J·g⁻¹, indicating no incompatibility with standard downstream drying temperatures.
| Temperature (°C) | Product Yield (HPLC area-%) | Protodebromination By‑product (area-%) | Unreacted Bromo Ester (area-%) |
|---|---|---|---|
| 85 | 92.3 | 1.1 | 4.8 |
| 95 | 94.8 | 2.9 | 1.2 |
| 100 | 78.2 | 15.6 | 3.1 |
| 110 | 41.7 | 48.3 | 2.8 |
The sharp jump in protodebromination at 100–110 °C is consistent with a Pd‑hydride β‑elimination pathway that becomes kinetically competitive when the amine concentration in solution is depleted; switching the base to Cs₂CO₃ reduced debromination at 110 °C to 22 % but converted the ester to the carboxylic acid in 17 % HPLC yield. Therefore, maintaining a ≤±3 °C deviation from the set point of 95 °C with a high‑surface‑area condenser and controlled pressure (N₂ blanket at 0.2 bar gauge) is essential for obtaining reproducible >90 % isolated yields on a multi‑kilogram scale. Process analytical technology (in‑line ReactIR monitoring of the C=O stretch at 1725 cm⁻¹) provides real‑time confirmation that intermediate acyl‑palladium complexes persist without decomposing.
A typical pharmaceutical‑grade specification for methyl 2‑bromo‑1,3‑thiazole‑5‑carboxylate used in early‑phase GMP synthesis is summarized in Table 2. The methods are harmonized with compendial references as noted. Residual solvent limits follow ICH Q3C options for Class 2 solvents; common process solvents such as dichloromethane and THF are monitored by headspace GC‑FID using a DB‑624 column (30 m × 0.32 mm, 1.8 µm). Elemental impurities are controlled to the ICH Q3D Option 1 permitted daily exposure values for oral drug products; arsenic, cadmium, mercury, and lead are quantified by ICP‑MS after microwave digestion. The polymorphic form is confirmed by X‑ray powder diffraction (XRPD) against a reference pattern; no solvates or hydrates have been detected upon crystallization from ethyl acetate/heptane.
| Parameter | Acceptance Criterion | Test Method |
|---|---|---|
| Appearance | White to off‑white crystalline powder | Visual Inspection |
| Identification | ¹H‑NMR spectrum conforms to reference at 400 MHz; IR spectrum matches reference | USP <197K>, USP <197M> |
| Assay (anhydrous, solvent‑free) | 98.5–101.5 % | HPLC, USP <621> |
| Melting Range | 62–66 °C | USP <741> Class I |
| Water (K. Fischer) | ≤ 0.5 % | USP <921>, Method 1a |
| Residual Solvents | Methanol ≤ 3000 ppm, THF ≤ 720 ppm, DCM ≤ 600 ppm, Ethyl acetate ≤ 5000 ppm | GC‑HS, USP <467> Procedure A |
| Heavy Metals (Pb, Cd, Hg, As) | Each ≤ 10 ppm | ICP‑MS, USP <233> |
| Purity (HPLC) | Any individual impurity ≤ 0.5 %, total impurities ≤ 1.5 % | HPLC, USP <621> |
| Residue on Ignition | ≤ 0.1 % | USP <281> |
Notably, the dibrominated analog (2,5‑dibromo‑1,3‑thiazole) and the regioisomeric methyl 5‑bromo‑1,3‑thiazole‑2‑carboxylate are the most common process impurities; the HPLC method using a C18 column (150 mm × 4.6 mm, 3 µm) with a gradient of acetonitrile/water + 0.1 % TFA achieves baseline separation with a resolution ≥ 2.0 between the target compound and methyl 5‑bromo‑1,3‑thiazole‑2‑carboxylate at relative retention time 1.31. A dedicated system suitability test requires a tailing factor ≤ 2.0 and theoretical plates ≥ 10,000 for the main peak.
Direct C–H arylation of thiazole substrates often relies on the presence of a leaving group at the 2‑position to direct the palladation event. The bromo ester exhibits superior regioselectivity compared to the chloro ester in C‑2 selective direct arylation with aryl bromides. Using a catalytic system of Pd(OAc)₂ (5 mol%), PivOH (30 mol%), and K₂CO₃ (2.0 equiv) in DMAc at 100 °C under air, the bromo ester gave the 2,5‑diaryl product in 76 % isolated yield; under identical conditions, the chloro ester produced 52 % yield with 18 % of the homo‑coupled 5,5′‑dimer. The higher bond dissociation energy of the C–Cl bond (ΔE ≈ 13 kcal·mol⁻¹ greater) retards the oxidative addition step, allowing a competing Pd(II)/Pd(IV) pathway to generate the homocoupling off‑pathway. Mechanistic investigations by Pregosin and co‑workers on related 2‑haloazoles suggest that the bromo derivative forms a transient κ²‑Br,Pd intermediate that facilitates C–H activation at the adjacent 5‑position; the chloride lacks this templating effect. While published kinetic data for this specific substrate remain limited, online reaction monitoring (ReactIR) of the C=O stretching frequency revealed an induction period of approximately 20 min for the bromo ester versus 55 min for the chloro analogue, consistent with faster pre‑catalyst activation. Temperature ramping above 120 °C should be avoided because the ester moiety undergoes palladium‑catalyzed decarbonylation with formation of methyl 2‑bromo‑1,3‑thiazole, an impurity that co‑distills during solvent swap and complicates polymorph control in subsequent steps.
Medicinal chemistry campaigns leverage methyl 2‑bromo‑1,3‑thiazole‑5‑carboxylate as a key intermediate for analogues of angiotensin II receptor blockers, kinase inhibitors (where it replaces a benzothiazole scaffold), and antifungal azole agents. The regioisomer methyl 5‑bromo‑1,3‑thiazole‑2‑carboxylate places the ester at the 2‑position and the bromine at 5, reversing the vector geometry of the eventual biaryl linkage; this difference in substitution pattern directly influences the dihedral angle of the downstream molecule and thereby its binding pose, as shown by X‑ray structures of human MAP4K4 inhibitors with either regioisomer. For in‑house lead optimization, small‑scale (50 g) batches are customarily synthesized via a Sandmeyer‑type halogenation of the corresponding 2‑aminothiazole‑5‑carboxylate ester using CuBr₂ and tert‑butyl nitrite in acetonitrile at 0–5 °C, circumventing the need for elemental bromine and delivering an >85 % yield after recrystallization.
