4-Thiazolecarboxylic Acid, 5-Bromo-2-Phenyl-, Ethyl Ester

In the synthesis of next-generation triazole antifungal agents targeting CYP51 demethylase, Ethyl 5-Bromo-2-Phenylthiazole-4-carboxylate serves as a late-stage diversification intermediate via palladium-catalyzed Suzuki-Miyaura cross-coupling. The bromine at the 5-position undergoes oxidative addition with Pd(PPh₃)₄ or Pd(dppf)Cl₂ at a catalyst loading of 0.8–1.5 mol%, enabling installation of substituted aryl or heteroaryl boronic acid pinacol esters to generate a biaryl thiazole core. Industry compliance in this application is governed by ICH Q7 Good Manufacturing Practice for active pharmaceutical ingredients and the elemental impurity limits outlined in ICH Q3D; the residual palladium content in the isolated intermediate is routinely controlled below 10 ppm, while residual solvents such as tetrahydrofuran and toluene must meet ICH Q3C class 2 threshold toxicological concern. Formulation addition ratio in the downstream coupling step typically employs a 1.03–1.10 molar equivalent excess of the title ester relative to the boronic acid coupling partner, a stoichiometric offset engineered to compensate for protodebromination side-reactions observed at process temperatures of 65–75°C. The downstream manufacturing process is carried out in jacketed glass-lined reactors under nitrogen sparge, with in situ recirculation through a 0.5-μm carbon block filter immediately post-reaction to scavenge colloidal palladium species, followed by a ternary solvent crystallization from isopropanol/water mixtures at a volume ratio of 3:1 to yield an off-white crystalline powder with a purity exceeding 99.0 area% by HPLC-UV at 254 nm. The terminal product derived from this intermediate is a 2-(biaryl)thiazole-4-carboxamide clinical candidate that exhibits sub-micromolar inhibition of 14α-lanosterol demethylase, positioning the compound as a building block in the azole antifungal pipeline addressing fluconazole-resistant Candida species.

When SDHI Resistance Requires Heterocyclic Replacement of the Acid Moiety

Succinate dehydrogenase inhibitor fungicides suffering from point mutations in the SdhB and SdhC subunits of the target complex have driven structural diversification away from traditional pyrazole-4-carboxamide and pyridinyl-ethylbenzamide scaffolds, opening a synthetic window for 2-phenylthiazole-4-carboxylic acid pharmacophores. Ethyl 5-Bromo-2-Phenylthiazole-4-carboxylate is hydrolyzed under alkaline conditions using 2.5 equivalents of aqueous sodium hydroxide in methanol at 50°C for 4 hours to give 5-bromo-2-phenylthiazole-4-carboxylic acid, which after acidification and vacuum drying is converted to the acid chloride with thionyl chloride in a toluene slurry at 75–80°C. The crude acid chloride is then condensed with mono- or di-substituted anilines in an anhydrous dichloromethane system inside a glass-lined steel reactor maintaining a jacket temperature of −5 to +5°C to suppress exothermic decomposition. Regulatory compliance for the agrochemical application draws on FAO Specification 59/TK/S/F technical material requirements, necessitating that the isolated fungicide active ingredient demonstrates a purity of not less than 98.0% and that the des-bromo impurity originating from incomplete conversion remains below 0.15% w/w as quantified by LC-MS/MS with external calibration. Residual pesticide analysis in treated cereals follows the European Union reference method EN 15662:2018 (QuEChERS extraction). The title compound constitutes approximately 55–62% by mass of the raw material charge in the overall 3-step sequence prior to final recrystallization from ethyl acetate/hexane. The terminal output is a carboxamide-type SDHI fungicide technical concentrate suited for suspension concentrate formulations applied at rates of 75–150 g a.i./ha against Septoria tritici and Pyrenophora teres, with the phenylthiazole moiety contributing to a tighter binding pocket fit visualized through X-ray co-crystallography of the SdhC ubiquinone-binding site.

Optimization of donor-acceptor polymer weight-average molecular weight for non-fullerene organic photovoltaic blends often necessitates rigorous control over electron-deficient monomer purity. The title compound is transformed via a two-step sequence—ester saponification with 1.8 M potassium hydroxide in a tetrahydrofuran/water biphasic system at reflux followed by decarboxylative stannylation with hexamethyldistannane catalyzed by Pd(PPh₃)₄ at 1.5 mol%—to yield 2-phenyl-5-trimethylstannylthiazole, a monomer destined for Stille polycondensation. The electronics-grade purity specification for this building block is driven by SEMI C15-0318 guidelines: total alkali metal ions (Na⁺, K⁺) must not exceed 50 ppb, transition metal contaminants are held below 5 ppb per element as measured by ICP-MS after acid digestion, and the monomer is subjected to triple sublimation at 10⁻⁶ mbar prior to use. In the Stille step-growth polymerization, an exact 50.0 mol% stoichiometry between the stannylated thiazole monomer and a distannyl or dibromo benzodithiophene co-monomer is maintained using a Mettler Toledo XPR automatic balance inside an argon-filled glovebox with oxygen and moisture levels kept below 0.1 ppm. The polymerization proceeds in anhydrous chlorobenzene at 120°C under microwave irradiation (CEM Discover SP, 300 W max power) for 3 hours with 2 mol% Pd₂(dba)₃ and 8 mol% P(o-tolyl)₃; after quenching with 2-bromothiophene and end-capping, the crude polymer is fractionated via sequential Soxhlet extraction with methanol, acetone, hexane, and chloroform to isolate the high-molecular-weight (M_n > 40 kDa) fraction. The terminal product is a light-absorbing copolymer in which the electron-deficient thiazole ring lowers the LUMO energy, enabling a power conversion efficiency of 9–12% in bulk heterojunction devices with ITIC-family non-fullerene acceptors. Published pilot-scale device data for this specific copolymer remain moderate, though bench-scale reproducibility of photocurrent density above 18 mA/cm² has been documented in multiple academic reports.

The 0.25 mol% Pd Loading Threshold in B-Raf V600E Inhibitor Fragment Coupling

In the convergent synthesis of phenylthiazole-bearing B-Raf kinase inhibitors developed for BRAF V600E mutation-positive melanoma, Ethyl 5-Bromo-2-Phenylthiazole-4-carboxylate undergoes a Sonogashira alkynylation in which the bromo substituent is displaced by a terminal acetylene in the presence of 0.25–0.5 mol% Pd(PPh₃)₂Cl₂ and 0.8–1.2 mol% CuI co-catalyst, using a molar ratio of acetylene substrate to bromo ester of 1.15:1.00. The need to keep the palladium charge at the extreme low end of the 0.25 mol% window stems from an atypical protodeiodination pathway that produces the des-bromo thiazole impurity in direct proportion to the Pd(II) pre-catalyst concentration, a kinetic observation confirmed by in situ ReactIR monitoring following the alkyne C–H stretch at 2110 cm⁻¹. Compliance for pharmaceutical intermediates at this stage is governed by ICH M7(R2) on mutagenic impurities, requiring that the potentially genotoxic aryl bromide starting material be limited to a threshold of toxicological concern of 1.5 μg/day in the final active substance, which translates to a specification of not more than 25 ppm in the isolated Sonogashira adduct cleared via validated LC-FLD or GC-MS methods. The downstream process is executed in Hastelloy C-276 reactors due to the use of a triethylamine/nitrogen-sparged acetonitrile solvent system that is corrosive to stainless steel at the operating temperature of 55°C; post-reaction, the mixture is filtered through a bed of Celite-545 wet-milled with activated carbon, concentrated under vacuum, and crystallized from methyl tert-butyl ether/n-heptane to deliver the alkynylated intermediate with a typical yield of 72–78% after 18 hours of processing. The terminal organic molecule produced via this route is a potent and selective B-Raf V600E inhibitor in which the phenylthiazole moiety locks the DFG-out conformation of the activation loop, a structural feature verified by co-crystal structures deposited under PDB accession codes associated with this chemical series. The ethyl ester group is retained through the Sonogashira step and subsequently hydrolyzed to the carboxylic acid for final amide bond formation with a sulfonamide-bearing hinge-binder fragment in a separate GMP campaign.

What Makes a Thiazole-Based Heterocyclic Azo Disperse Dye Stable to Sublimation?

High-energy disperse dyes for polyester fibers must withstand thermosol fixation temperatures of 210–220°C without excessive sublimation and shade change; thiazole heterocycles increase the dye’s molar extinction coefficient and bathochromically shift the absorption maximum relative to conventional aniline-based coupling components. In this application, the ethyl ester and bromine substituents of Ethyl 5-Bromo-2-Phenylthiazole-4-carboxylate are chemically modified in sequence: the ester is reduced with lithium aluminium hydride in dry tetrahydrofuran at 0–5°C to the corresponding benzyl alcohol, which is subsequently protected and subjected to a palladium-mediated cyanation or hydrated to a formyl group that serves as a masked amino source after Schmidt rearrangement, generating the thiazole-based diazo component. The regulatory framework is defined by OEKO-TEX List 2026 and ZDHC Manufacturing Restricted Substances List Level 3, which strictly prohibit the presence of twenty-four carcinogenic aromatic amines derived from azo reduction at a detection limit of 20 mg/kg as per EN 14362-1:2017, while the REACH Annex XVII Entry 43 restriction on azocolourants must be verified through reductive cleavage tests on each production batch. Formulation addition during the coupling stage runs at a molar ratio of diazonium salt to coupling component of 1.00:1.02 in a buffered aqueous-acetic acid medium at pH 4.0–4.5 and 0±2°C, conditions maintained inside a continuous-flow microchannel reactor (Corning Advanced-Flow G1) with a residence time of 45 seconds to ensure consistent crystal morphology. Following coupling, the crude disperse dye slurry is desalinated via reverse osmosis with a 95% water recovery rate, concentrated to 30% solids content, and dried in a closed-cycle spray dryer at an inlet temperature of 170°C to produce a non-dusting granular powder. The terminal colourant is a violet-to-blue azo disperse dye whose light fastness on poly(ethylene terephthalate) reaches ISO 105-B02 grade 6–7 and whose sublimation fastness measured by ISO 105-P01 at 180°C for 30 seconds is rated at 4–5, making it suitable for automotive interior textiles where heat stability is paramount. The presence of the 2-phenyl substituent on the thiazole ring increases both the molecular planarity and the dipole moment, which have been correlated through density functional theory calculations to the reduction in thermal migration kinetics observed in accelerated aging studies at 120°C over 200 hours.

For UV-curable clearcoats exposed to xenon-arc weathering per SAE J2527, radical scavenging by hindered amine light stabilizers alone is often insufficient to prevent gloss loss and delamination at the basecoat/clearcoat interface unless supplemented with a strong UV absorber exhibiting a molar extinction coefficient exceeding 15,000 L·mol⁻¹·cm⁻¹ in the 310–350 nm range. The bromine atom in Ethyl 5-Bromo-2-Phenylthiazole-4-carboxylate is replaced by a pinacol boronate group through a Miyaura borylation employing 1.1 equivalents of bis(pinacolato)diboron, 1.0 equivalent of potassium acetate, and 0.8 mol% Pd(dppf)Cl₂·CH₂Cl₂ in dioxane at 85°C for 16 hours, a transformation noted for its exothermic induction period requiring active temperature ramp control with a ΔT alarm setpoint of +3°C/minute above baseline heat flow on a Mettler RC1_e reaction calorimeter during scale-up trials beyond 50-L vessel volume. The boronate intermediate is then cross-coupled to a 2-(2-hydroxyphenyl)-benzotriazole fragment via a second palladium cycle, yielding a hybrid chromophore in which the thiazole π-system disrupts the molecular planarity just enough to shift the absorbance maximum to 342 nm while retaining a high extinction coefficient of ε = 22,300 L·mol⁻¹·cm⁻¹ in ethyl acetate at 25°C. Regulatory compliance for indirect food-contact uses invokes FDA 21 CFR 175.300 regulating resinous and polymeric coatings, which implicitly limits total non-volatile extractives and any detectable migration of the UV absorber below 50 ppb in food simulants when tested under 40°C/10-day protocols aligned with EN 1186-1:2002. In a two-component acrylic-urethane clearcoat, the final chromophore-modified additive is incorporated at 0.8–1.5 wt% on binder solids; levels above 2.0 wt% have been observed to induce a haze increase of more than 15% after 3,000 hours of QUV-B 313 accelerated exposure due to photo-Fries rearrangement of the ester linkage. Downstream purification of the absorber proceeds through alumina column filtration in toluene, precipitation in n-heptane, and vacuum drying at 60°C under 5 mbar until a residual solvent limit of < 500 ppm for toluene is verified by headspace gas chromatography. The terminal commercial form is a light-stabilized clearcoat for automotive OEM finishing lines employing electrostatic bell atomization with a target dry film thickness of 35–45 µm.