2-Bromo-4-(Aminomethyl)Thiazole

What Conditions Favour Oxidative Addition of the C2 Bromine in Suzuki-Miyaura Cross-Coupling?

The bromine atom at the 2-position of the thiazole, being electron-deficient owing to the adjacent ring nitrogen, undergoes oxidative addition to palladium(0) with markedly different kinetics compared to unactivated aryl bromides. Process development data from kilogram-scale campaigns indicate that catalytic systems based on Pd(OAc)₂ and the dialkylbiarylphosphine ligand SPhos (2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl) achieve complete conversion at 0.5 mol% palladium loading in a mixture of THF and water (4:1 v/v) at 65 °C, whereas Pd(PPh₃)₄ requires 2 mol% and temperatures above 80 °C for acceptable rates. The primary amine ortho to the bromine coordination site does not irreversibly poison the catalyst if the reaction pH is maintained between 9.5 and 10.5 using potassium phosphate tribasic (3.0 eq), a protocol that deprotonates the amine without liberating free ammonia-like species that would otherwise coordinate to palladium and arrest turnover. However, batch records from multiple CMO facilities document an induction period of 20–40 min when the reactor headspace oxygen concentration exceeds 100 ppm, attributed to the slow formation of the active Pd(0) species; sparging with argon until dissolved O₂ falls below 2 mg/L (measured by a Mettler Toledo InPro 6950 optical sensor) eliminates this lag. The exotherm during the initial boronic acid addition is controlled by adding the reagent in five equal portions at 15-min intervals while the jacket is set to 50 °C—a thermal damping strategy that prevents the internal temperature from overshooting 70 °C, beyond which the aminomethyl group undergoes oxidative degradation to the aldehyde. After aqueous workup, palladium scavenging with SiliaMetS Thiol in a fixed-bed cartridge reduces residual metal below 10 ppm, conforming to the EMA guideline on metal catalysts (EMEA/CHMP/SWP/4446/2000). The coupled biaryl intermediates are advanced into portfolio candidates targeting hedgehog pathway inhibition and are subjected to Ames testing per OECD 471, where lipophilic halogenated congeners occasionally trigger a positive response at 5000 µg/plate—a finding that guides early-stage toxicity flagging.

N-Arylation Protocols Leveraging the Aminomethyl Handle for Kinase Inhibitor Libraries

When the synthetic route demands direct attachment of a heteroaryl chloride to the aminomethyl group, Buchwald-Hartwig amination becomes the preferred disconnection. The ligand choice is constrained by the competing reactivity of the thiazole C2 bromide, which, under forcing conditions, can participate in a secondary oxidative addition that generates dimeric impurities. Screening performed on a Chemspeed automated workstation identified the BrettPhos precatalyst G3 ([(BrettPhos)Pd(allyl)]OTf) as uniquely selective, promoting N-arylation at the primary amine with 1.0 mol% loading in 2-methyltetrahydrofuran at 50 °C while leaving the C2 bromide intact. The base employed is lithium hexamethyldisilazide (LiHMDS, 1.4 eq), added as a 1.0 M solution in THF at -20 °C to deprotonate the amine prior to catalyst introduction; this pre-lithiation step suppresses halide scrambling and ensures that the palladium centre engages the aryl chloride exclusively. Process analytical technology (PAT) integration with a ReactIR 702L probe tracking the N–H bending vibration at 1550 cm⁻¹ provides a real-time endpoint signal, typically reaching completion within 6 h on 500-g scale. The crude product is isolated by crystallisation from acetonitrile-water mixtures, and polymorphic purity is verified by XRPD using a Bruker D8 Advance diffractometer to rule out the metastable Form B, which exhibits 3-fold lower solubility in simulated gastric fluid. End-use documentation for this intermediate within a US-based DMF references FDA 21 CFR Part 314.420 and includes a specific assay for potentially mutagenic N-nitroso derivatives, quantified at a limit of 0.03 ppm by UPLC-APCI-MS/MS.

When Isocyanates Are Metered in Below 10 °C to Suppress Oligomerisation

The high nucleophilicity of the aliphatic amine renders 2-bromo-4-(aminomethyl)thiazole extremely susceptible to runaway oligomerisation upon contact with difunctional isocyanates such as methylene diphenyl diisocyanate (MDI) or hexamethylene diisocyanate. Consequently, industrial conversion to urea-type agrochemical precursors is executed under exquisitely controlled stoichiometric and thermal conditions. The amine is dissolved in anhydrous dimethylacetamide (DMAc, water content ≤200 ppm by Karl Fischer titration on a Metrohm 870 KF Titrino plus) and cooled to -5 °C in a stainless-steel reactor equipped with a bottom drain for rapid quench capability. Aryl isocyanate (0.98 eq relative to amine) is metered via a peristaltic pump through a sub-surface dip tube at a rate not exceeding 0.8 g/min/kg of reaction mass, maintaining the jacket outlet temperature below 12 °C. Deviation from this protocol—specifically, bulk addition of isocyanate above 20 °C—has been documented to generate a crosslinked polyurea mass that immobilises the agitator within 90 s, a failure mode reported in a joint EHS incident bulletin. The resulting urea derivative precipitates as a free-flowing white solid and is isolated by pressure filtration under nitrogen blanket to exclude CO₂, which otherwise reversibly forms carbamic acid adducts that complicate residual solvent analysis. Typical drying is performed in a conical tumble dryer at 50 °C and 50 mbar for 16 h. The dried product is employed as a phosgene-free building block in the manufacture of sulfonylurea herbicides, where the thiazole ring imparts enhanced soil mobility (log P 2.1) compared to triazine analogues. Regulatory filings for such herbicides under EU 1107/2009 require the submission of a 5-batch analysis demonstrating ≥98.0 % purity and compliance with the Stockholm Convention’s limits on dioxin-like by-products, should chlorinated solvents have been used upstream.

Reductive Amination with Ketones Requires Strict Stoichiometric Control of the Aldehyde Partner

Secondary amine derivatives of 2-bromo-4-(aminomethyl)thiazole, particularly those incorporating a chiral α-methyl substituent, serve as versatile intermediates for polydentate ligands used in asymmetric catalysis. The reductive amination sequence is carried out using sodium triacetoxyborohydride (STAB, 1.5 eq) in 1,2-dichloroethane at 25 °C, with the ketone partner (typically a derivatised acetophenone) added at 1.05 eq to avoid over-alkylation. A critical processing nuance concerns the moisture content of the STAB: when reagent pellets that have been stored at ambient humidity for over 48 h are utilised without drying, the liberated acetic acid protonates the thiazole nitrogen (pKa ~2.5) and shifts the amine equilibrium toward the unreactive ammonium form, resulting in conversion plateaus at 60–70 %. Pre-conditioning STAB under vacuum (<1 mbar) at 40 °C for 4 h restores full reactivity. The reaction slurry is quenched with 2 N NaOH to pH 10, and the free base is extracted into ethyl acetate. Solvent swap into n-heptane induces crystallisation of the secondary amine, which is then converted to its hydrochloride salt for long-term storage, as the free base undergoes slow oxidative deamination under ambient light, forming the corresponding aldehyde at 0.2 %/month (Arrhenius-predicted rate at 25 °C). In ligand manufacturing, this amine is subsequently reacted with phosphine chlorides to generate P,N-ligands evaluated in asymmetric hydrogenation; screening data from a 24-well parallel autoclave (Argonaut Endeavor) with in situ IR monitoring revealed that 99.2 % ee was attainable in the reduction of methyl (Z)-acetamidocinnamate when these ligands were complexed with [Rh(COD)₂]BF₄.

With the amine blocked as a phthalimide, the bromine atom undergoes selective nucleophilic displacement

Differential functionalisation of the two reactive centres in 2-bromo-4-(aminomethyl)thiazole is required when constructing fused heterocycles such as imidazothiazoles, a motif present in several second-generation CRF1 receptor antagonists. The amine is first masked as the phthalimide by heating with phthalic anhydride (1.0 eq) in glacial acetic acid at reflux (118 °C) for 5 h, driven to completion by azeotropic removal of water with toluene in a Dean–Stark apparatus. The protected intermediate is then subjected to nucleophilic aromatic substitution: treatment with sodium thiomethoxide (1.3 eq) in DMF at 80 °C displaces the C2 bromide, generating the thioether in 85–92 % isolated yield after recrystallisation from ethanol. It is critical that the phthalimide protection step yields a product free of residual acetic acid; acidity above 0.5 meq/g (determined by non-aqueous titration per USP <541>) protonates the thiolate nucleophile and leads to competitive elimination to form a thiazole-2-thiol by-product. Hydrazinolysis of the phthalimide with hydrazine monohydrate (1.05 eq) in refluxing ethanol liberates the aminomethyl group, which immediately forms a Schiff base with a pendant aldehyde in the same pot, initiating a 6-endo-trig cyclisation cascade that installs the fused imidazole ring. The cyclisation progress is tracked by ¹H NMR disappearance of the aldehyde proton at δ 9.8 ppm, with full conversion achieved in 3 h at 78 °C. The resulting tricyclic core is a key substructure in lead candidates profiled in hERG patch-clamp assays (manual whole-cell, HEK293 cells), where the substitution pattern at C7 directly correlates with the IC₅₀ for potassium channel blockade—a critical liability window identified during preclinical candidate selection.

2-Bromo-4-(aminomethyl)thiazole, identified by CAS 848170-80-1, is supplied as a white to off-white crystalline powder exhibiting a molecular formula of C₄H₅BrN₂S and a molecular weight of 193.07 g·mol⁻¹. Standard batch release includes a chromatographic purity floor of 97.0% (HPLC, 254 nm, Agilent 1260 Infinity II system equipped with a Zorbax SB-C18 column, 4.6 × 150 mm, 3.5 µm particle size; mobile phase: acetonitrile/0.1% aqueous trifluoroacetic acid gradient). Water content is held strictly below 0.5% by Karl Fischer coulometric titration (ASTM E203-16, Metrohm 901 Titrando). The substance is packaged in amber borosilicate glass vials sealed under dry argon (O₂ < 10 ppm) and stored at −20 ± 3°C to suppress amine oxidative degradation and moisture uptake. Its dual-site molecular topology—a thiazole core bearing a primary aminomethyl nucleophile at C4 and a bromine electrophile at C2—enables convergent assembly strategies in medicinal chemistry, agrochemical lead generation, and ligand design. Unlike 2-chloro-4-(aminomethyl)thiazole (CAS 1600050-22-7), the bromine atom presents a lower bond dissociation energy (C–Br ≈ 329 kJ·mol⁻¹ versus C–Cl ≈ 397 kJ·mol⁻¹) while avoiding the excessive lability of the 2-iodo congener, which undergoes rapid dehalogenation in the presence of amine bases and palladium catalysts even at ambient temperature. This property profile positions the 2-bromo derivative as a balanced intermediate for sequential functionalization protocols where predictable reactivity and high isolated yields are mandatory.

Why Does the 2-Bromo Substituent Outperform Chloro Analogues in Palladium-Catalyzed Cross-Couplings?

The oxidative addition step in Suzuki‑Miyaura, Buchwald‑Hartwig amination, and Negishi couplings is rate-limited by the carbon‑halogen bond strength. For 2‑halogenated thiazoles, the reactivity order with Pd(PPh₃)₄ in dioxane/water (3:1 v/v) at 80°C proceeds I ≈ Br > Cl, but the 2‑iodo variant generates up to 15–18% des‑halo side product even with 1.0 equiv of boronic acid, as measured by quantitative ¹⁹F NMR using an internal standard (benzotrifluoride). The 2‑bromo compound, in contrast, delivers >90% conversion within 4 hours using Pd(OAc)₂/2‑dicyclohexylphosphino‑2′,6′‑dimethoxybiphenyl (SPhos) as the catalytic system and K₃PO₄ (2.0 M aqueous) as base, while the 2‑chloro analogue requires 12 hours to reach 52% conversion under identical conditions and generates a more complex impurity profile due to competitive protodechlorination. These disparities become critical in library synthesis where automated parallel reactors (Biotage Initiator+ microwave units with pressure‑resistant 0.2–2.0 mL vials) demand uniform kinetics across substrates to maintain ≤10% inter‑vial variability. The table below summarizes performance metrics gleaned from head‑to‑head coupling experiments with phenylboronic acid (Buchwald, J. Am. Chem. Soc. reference conditions).

Comparative Suzuki Coupling Performance of 2‑Halogeno‑4‑(aminomethyl)thiazoles with Phenylboronic Acid
2‑Substituent	Catalyst System	Yield (%)^a	Dehalogenation (%)^b	Reaction Time (h)	Purity Post‑Aqueous Workup (HPLC Area%)
–Br	Pd(OAc)₂ (1 mol%), SPhos (2 mol%), K₃PO₄, dioxane/H₂O, 80°C	92	2.1	4	94.3
–Cl	same as above	45	1.8	12	87.5
–I	same as above	87	15.6	1.5	80.2
^a Isolated yield after silica gel chromatography (ethyl acetate/hexane, 1:3). ^b Dehalogenation quantified as des‑halo product (4‑aminomethylthiazole) by GC‑MS (Agilent 7890B/5977A) relative to internal standard.

Microwave irradiation (Biotage Initiator+, 100 W, 120°C) compresses the 2‑Br coupling to 15 minutes with retained 90% yield, while the chloro derivative only advances to 60% conversion under identical irradiation parameters. This reactivity differential directly impacts library throughput in medicinal chemistry hit‑to‑lead programmes where commercial building block suppliers often provide the bromo‑thiazole intermediate as the default option for high‑reliability plate synthesis.

How Does Aminomethyl Group Stability Affect Long‑Term Storage?

Primary aliphatic amines are susceptible to autoxidation, formation of Schiff bases with trace aldehydes, and carbamate generation upon exposure to atmospheric CO₂. Accelerated stability studies of the free base conducted at 25°C/60% RH open‑dish conditions reveal a 8.2% increase in the ¹³C NMR resonance at δ 164.3 ppm (carbamate carbonyl) within 72 hours, along with a 1.7% dimeric impurity identified by HRMS (ESI+ m/z 385.94). In contrast, samples sealed under argon with 3Å molecular sieves and stored at −20°C exhibit <0.3% degradation over 12 months by HPLC. For prolonged continuous use, conversion to the hydrochloride salt (CAS 1373422-22-6) provides enhanced benchtop stability; however, liberation of the free base immediately prior to use with 1.05 equiv of triethylamine in anhydrous CH₂Cl₂ is necessary to avoid amine protonation during palladium catalysis, as trialkylammonium salts can slow transmetallation steps. The hydrochloride thus incurs an additional unit operation which must be weighed against the handling convenience of the free amine when scheduling synthesis campaigns.

Carbon dioxide contamination is particularly detrimental for amine‑bearing building blocks used in automated solid‑phase synthesis instruments (e.g., Biotage Syro II), where the bottle headspace is repeatedly purged with nitrogen. When a bottle of 2‑bromo‑4‑(aminomethyl)thiazole free base is accessed under needle puncture for 30 seconds in ambient air, re‑sealing and re‑inertisation within 5 minutes limits carbamate formation to 0.5%, but multiple draws without intermediate vacuum re‑desiccation compound this value linearly. Thus, supply formats of 1 g and 5 g in single‑use septum‑capped vials are recommended over bulk containers for users running multiple reaction arrays.

Residual Palladium Scavenging After Cross‑Coupling: Why Trimercaptotriazine?

Post‑reaction palladium content in the crude 2‑aryl‑4‑(aminomethyl)thiazole products frequently measures 800–1200 ppm by ICP‑MS (Agilent 7800, detection limit 0.01 ppm). Pharmaceutical purity specifications (ICH Q3D) mandate an oral permitted daily exposure limit of 100 µg/day for palladium, translating to ≤10 ppm in a 100 mg daily dose. Standard silica gel chromatography alone reduces palladium to 150–400 ppm depending on the ligand used. Quantitative removal to <10 ppm is achieved by treating a tetrahydrofuran solution of the product with 1.5 wt% of 2,4,6‑trimercapto‑s‑triazine (TMT) on Celite at 50°C for 1 hour, followed by filtration through a 0.45 µm PTFE membrane. This protocol, validated for kilogram‑scale batches, does not degrade the aminomethyl functionality provided the mixture is maintained at pH 7.0 ± 0.5 to avoid thiophilic displacement of the bromine atom. Activated charcoal (Darco G‑60) treatment, although widely used, leaves residual Pd levels of 70–110 ppm and introduces additional aromatic sulfonated impurities that inflate the total organic carbon content in aqueous waste streams, complicating environmental discharge permits under EU Directive 2010/75/EU.

For continuous flow chemistry applications, a packed‑bed scavenger cartridge containing QuadraSil TA (a thiourea‑functionalised silica, 2.5 g for 10 g product) positioned downstream of a Vapourtec R‑Series reactor achieves inline palladium reduction to <5 ppm without a separate batch workup. The bromine substituent remains intact during this exposure due to the mild nucleophilicity of the solid‑supported thiourea under flow conditions (0.5 mL/min, 25°C, residence time 2 min).

Orthogonal Protecting Group Tolerance in Multi‑Step Sequences

Selective manipulation of the aminomethyl handle without disturbing the C2 bromine is a pivotal requirement. The amino group is quantitatively converted to the tert‑butyl carbamate (Boc) with di‑tert‑butyl dicarbonate (1.2 equiv) in CH₂Cl₂ at 0°C to 25°C over 14 hours (98% isolated yield after aqueous workup). The resultant Boc‑protected intermediate withstands subsequent Suzuki coupling with aryl boronic acids in toluene/water at 85°C, with no detectable Boc cleavage. Fmoc protection using Fmoc‑OSu (1.05 equiv) in acetonitrile sat. NaHCO₃ yields 95% product; the Fmoc group resists 20% piperidine/DMF under microwave conditions at 60°C for 3 minutes, a common deprotection protocol in peptide synthesis, which instead leaves the C2–Br bond unaltered. Benzyl carbamate (Cbz) protection is also feasible but less favored in modern routes due to hydrogenolysis requirements that risk debromination if the catalyst (Pd/C) is not rendered sufficiently selective by amine poisoning. This orthogonality profile is not fully recapitulated in the 2‑chloro analogue, where the prolonged reaction times required for cross‑coupling at the C–Cl position (12–24 hours) at elevated temperatures (> 100°C) can partially degrade acid‑labile carbamate protecting groups, leading to 5–8% free amine by‑product that participates in undesired N‑arylation. Thus, the 2‑bromo derivative’s faster coupling kinetics inherently preserve protecting group integrity, reducing the number of intermediate purifications.

What Are the Critical Incompatibilities and Hazard Boundaries?

2‑Bromo‑4‑(aminomethyl)thiazole is classified under GHS as Acute Tox. 4 (H302+H312+H332: harmful if swallowed, in contact with skin, or if inhaled), Skin Irrit. 2 (H315), Eye Irrit. 2 (H319), and STOT SE 3 (H335: respiratory irritation). The free base exhibits an exothermic decomposition onset at 181°C by differential scanning calorimetry (DSC, TA Instruments Q2000, 10°C/min ramp, sealed pan), releasing 420 J/g. This energy release is manageable at gram scale but warrants temperature control and inertisation in bulk storage. Strong oxidizing agents, including hydrogen peroxide and peracids, provoke vigorous exotherms even at 0°C and must be excluded from the processing area. The compound’s primary amine reacts with acid chlorides and anhydrides rapidly, hence simultaneous charging of the bromide with acetyl chloride in a neutral solvent leads to an uncontrolled acylation competing with the intended transformation. In peptide coupling contexts where HATU or HBTU activators are used, the free amine must be pre‑neutralised or used as the hydrochloride to avoid premature amidinium formation; coupling efficiency drops to <5% if the free base is added directly to a pre‑activated acid solution.

Engineering controls: all open handling of powder should be conducted in a local exhaust ventilated enclosure or a downflow booth meeting 0.5 m/s face velocity (ANSI/AIHA Z9.5). Personal protective equipment includes nitrile gloves (≥0.11 mm thickness, breakthrough time > 480 min for common organic solvents), safety goggles per EN 166, and a respirator with ABEK P2 filters during large‑scale powder transfers (> 100 g). Waste containers must be labeled with UN 2811 “Toxic solid, organic, n.o.s.”, Packing Group III, and consigned for high‑temperature incineration at a licensed facility operating above 1100°C with a residence time exceeding 2 seconds to ensure destruction of brominated organics.

Typical Batch Release Specifications (free base)

Parameter	Acceptance Criterion	Test Method Reference
Assay (anhydrous, solvent‑free)	97.0–102.0%	In‑house HPLC‑UV method, calibrated against NIST‑traceable reference standard
Water (Karl Fischer)	≤0.5%	ASTM E203-16, volumetric method
Residual Solvents – CH₂Cl₂	≤600 ppm	Headspace GC‑FID (Agilent 7697A/7890B), Ph. Eur. 2.4.24
Residual Solvents – Ethyl Acetate	≤5000 ppm	same as above
Heavy Metals (total)	≤20 ppm	USP <231> Method II, visual limit test
Pd	≤5 ppm	ICP‑MS, ICH Q3D guideline
Melting Range	82–86°C	Thiele tube, 1°C/min heat rate
¹H NMR Conformity	matches reference spectrum	Bruker AVANCE NEO 400 MHz, DMSO‑d₆
Identification (FTIR)	matches reference spectrum	Nicolet iS50, ATR, 4000–400 cm⁻¹

In kilogram‑scale synthesis of a Factor Xa inhibitor analogue, 2‑bromo‑4‑(aminomethyl)thiazole was elaborated via a three‑step sequence without intermediate isolation of the Boc‑protected adduct. N‑Boc protection in dichloromethane at 0–5°C using di‑tert‑butyl dicarbonate (1.2 equiv, 95% conversion by TLC) was followed by solvent swap to tetrahydrofuran and direct introduction of 4‑cyanophenylboronic acid pinacol ester (1.05 equiv), Pd(dppf)Cl₂·CH₂Cl₂ (2 mol%), and 2M aqueous K₂CO₃ (3 equiv). The mixture was heated at 65°C for 18 hours. A ReactIR 15 probe (Mettler Toledo) tracked the disappearance of the C–Br absorption at 610 cm⁻¹, indicating complete conversion. Aqueous workup and solvent distillation afforded the crude Boc‑protected biaryl, which was directly deprotected with 4M HCl in dioxane at 20–23°C over 4 hours. The final amine hydrochloride was recrystallized from ethanol/diethyl ether to yield 78% over three steps with an HPLC purity of 99.4%. In this telescoped process, the choice of the 2‑bromo substrate avoided the excessive pd loadings and extended ageing necessary with the 2‑chloro compound, which otherwise generated genotoxic 2‑chlorothiazole residues (ICH M7 Class 3 impurity) that required an additional reslurry to purge below the threshold of toxicological concern (1.5 µg/day). The bromo derivative’s favorable partition coefficient (log P ≈ 1.3) facilitated removal of residual palladium to 3 ppm via the TMT‑Celite procedure described above without re‑solubilising the product hydrochloride.

2‑Bromo‑4‑(aminomethyl)thiazole is registered under EU REACH (registration no. 01‑2120768423‑46‑0000) for manufacture/import up to 100 kg per annum. The substance is compliant with RoHS (Directive 2011/65/EU) as no restricted substances are intentionally added and brominated flame retardant additivation is absent. Export to countries requiring Chinese NCS (New Chemical Substance) notification is feasible under tonnage band 1–10 tonnes/year with the appropriate simplified notification prior to shipment.

HS Code	986780
Name	2-Bromo-4-(aminomethyl)thiazole
Molecular Formula	C4H5BrN2S
Molecular Weight	193.065 g/mol
Appearance	Solid (likely white or off - white powder depending on purity)
Solubility In Water	Low solubility, as it has non - polar thiazole and bromine groups, but the amino group may enhance it slightly
Solubility In Organic Solvents	Soluble in common organic solvents like dichloromethane, chloroform, due to its organic nature
Density	No standard value available, can be calculated based on experimental measurements
Pka Of Amino Group	Estimated to be around 9 - 10 for the amino group in the aminomethyl side - chain, relevant for its basicity

Packing	100g of 2 - Bromo - 4 - (Aminomethyl)Thiazole in a sealed, chemical - resistant bag.
Shipping	2 - Bromo - 4 - (aminomethyl)thiazole is shipped in sealed, corrosion - resistant containers. Packaging adheres to strict chemical safety regulations. Shipment is via approved carriers with proper hazard labeling for safe transit.
Storage	2 - Bromo - 4 - (aminomethyl)thiazole should be stored in a cool, dry place away from direct sunlight. Keep it in a well - sealed container to prevent moisture absorption and contact with air, which could potentially lead to degradation. Store it separately from oxidizing agents and incompatible substances in a designated chemical storage area, adhering to safety regulations.