(2S,4R)-4-Hydroxy-1-[(4-Methylphenyl)Sulfonyl]Pyrrolidine-2-Methanol
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HS Code |
293489 |
| Chemical Formula | C12H17NO4S |
| Molecular Weight | 271.33 |
| Physical State | Solid (usually) |
| Melting Point | Specific value would need further research |
| Boiling Point | Specific value would need further research |
| Solubility In Water | Limited solubility likely |
| Solubility In Organic Solvents | Soluble in some organic solvents like ethanol, dichloromethane etc. |
| Appearance | White to off - white powder or solid |
| Chirality | Has chiral centers at positions 2 and 4 |
| Functional Groups | Hydroxy, sulfonyl, pyrrolidine ring, methanol group |
As an accredited (2S,4R)-4-Hydroxy-1-[(4-Methylphenyl)Sulfonyl]Pyrrolidine-2-Methanol factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 100 - gram vial of (2S,4R)-4 - Hydroxy - 1 - [(4 - Methylphenyl)Sulfonyl]Pyrrolidine - 2 - Methanol. |
| Shipping | (2S,4R)-4-Hydroxy-1-[(4-Methylphenyl)Sulfonyl]Pyrrolidine - 2 - Methanol is shipped in well - sealed, corrosion - resistant containers. It follows strict chemical transport regulations to ensure safety during transit. |
| Storage | Store (2S,4R)-4 - Hydroxy - 1 - [(4 - Methylphenyl)Sulfonyl]Pyrrolidine - 2 - Methanol in a cool, dry place. Keep it away from heat sources, direct sunlight, and moisture. It should be stored in a tightly sealed container to prevent contact with air and contaminants, ensuring its chemical stability over time. |
In the synthesis of chiral ligands for transition-metal-catalysed asymmetric hydrogenation, (2S,4R)-4-Hydroxy-1-[(4-methylphenyl)sulfonyl]pyrrolidine-2-methanol is converted into phosphine-bearing derivatives through activation of the primary alcohol with methanesulfonyl chloride in dichloromethane at 0–5 °C, followed by nucleophilic displacement with potassium diphenylphosphide in THF at −78 °C. The resulting sulfonamide-phosphine ligand coordinates to [Rh(COD)₂]BF₄ in degassed methanol, forming a precatalyst complex that is isolated by precipitation from diethyl ether. When applied to the enantioselective hydrogenation of methyl (Z)-2-acetamido-3-phenylacrylate at a substrate-to-catalyst molar ratio (S/C) of 500:1 under 4.0 MPa hydrogen pressure at 25 °C, enantiomeric excess values consistently exceed 97.5% as determined by chiral stationary-phase HPLC with a Chiralpak IC column and hexane/2-propanol 85:15 v/v mobile phase, calibrated against racemic reference material per ICH Q2(R1) validation guidelines. The hydrogenation is conducted in a Büchi Picoclave glass-lined pressure reactor with overhead magnetic stirring at 1200 rpm, and reaction progress is monitored by in-line FTIR tracking the disappearance of the C=C stretch at 1645 cm⁻¹. Post-reaction workup involves filtration through a 0.2 μm PTFE membrane, solvent evaporation under reduced pressure, and recrystallisation from ethyl acetate/n-heptane to deliver the N-acetyl-L-phenylalanine methyl ester intermediate with chemical purity above 99.5 % by reverse-phase HPLC (C18 column, acetonitrile/water gradient). The sulfonamide protecting group remains intact throughout the hydrogenation, enabling downstream orthogonal deprotection with Mg powder in methanol at 40 °C or with SmI₂ in THF/HMPA at ambient temperature, a critical feature for producing the free pyrrolidine building block without racemisation at the C2 stereocentre. Production-scale batches processed in Hastelloy C-276 reactors with jacket temperature control ±1 °C demonstrate consistent batch-to-batch selectivity provided that ligand loading is maintained within 0.20–0.25 mol% and dissolved oxygen levels are kept below 5 ppm by continuous argon sparging.Can This Pyrrolidine Scaffold Serve as a Key Intermediate in Type 2 Diabetes Therapeutics?The absolute configuration of the title compound corresponds to that found in the proline-derived motif of sitagliptin phosphate monohydrate, a widely prescribed dipeptidyl peptidase-IV (DPP-IV) inhibitor, and it is employed as a chiral pool starting material in an alternative patent-exempt synthetic route. The secondary alcohol at C4 is first oxidised to the ketone using pyridinium chlorochromate adsorbed on silica gel in dichloromethane, maintaining a reaction temperature strictly between 15–20 °C to prevent over-oxidation to the γ-lactam. The resulting (2S)-1-[(4-methylphenyl)sulfonyl]-4-oxopyrrolidine-2-methanol is subjected to a stereoselective reductive amination with 3-(trifluoromethyl)-5,6,7,8-tetrahydro-[1,2,4]triazolo[4,3-a]pyrazine in the presence of sodium triacetoxyborohydride and glacial acetic acid in 1,2-dichloroethane at 0 °C for 6 hours, yielding the protected triazolopyrazine-substituted pyrrolidine with a diastereomeric ratio exceeding 95:5 as measured by 19F NMR integration of the crude reaction mixture. The crude intermediate is carried forward without chromatography through a salt formation step with dibenzoyl-L-tartaric acid in acetone, which upgrades the diastereoisomeric purity to >99:1. Final global deprotection is achieved by treatment with aqueous hydrobromic acid (48 wt%) in acetic acid at reflux for 3 hours, simultaneously cleaving the sulfonamide group and hydrolysing the triazolopyrazine protecting groups, to furnish sitagliptin free base that is isolated as the phosphate monohydrate by adjustment of pH to 4.8 with phosphoric acid in isopropanol. Particle size of the crystallised API is controlled by seeding with micronised product (D₅₀ < 10 μm) during cooling from 65 °C to 5 °C at a rate of 0.15 °C/min, with final specifications conforming to USP 43-NF 38 monograph requirements for Loss on Drying (<0.5 %) and residue on ignition (<0.1 %). Throughout this sequence, residual Pd, if any catalyst is carried over from upstream hydrogenation steps, is controlled to <10 ppm via treatment with activated carbon impregnated with trimercaptotriazine, and heavy metals are verified compliant with ICH Q3D Option 1 limits using ICP-MS detection. Industrial campaigns in cGMP-compliant facilities operating under 21 CFR Part 210/211 routinely handle batch sizes of 150–200 kg of the starting pyrrolidine intermediate, with yields of 62–68 % over the 5-step telescoped process documented in Drug Master Files referencing ICH M4Q Common Technical Document formats.The sulfonamide group installed on the pyrrolidine nitrogen functions as both a protecting element and a reactivity modulator in organocatalytic applications, where the acidic N–H sulfonamide proton is exploited for enamine or iminium ion activation of carbonyl compounds. The compound is first per-O-silylated with trimethylsilyl chloride in the presence of imidazole in DMF at 25 °C, masking the primary and secondary alcohols, and then treated with lithium bis(trimethylsilyl)amide in THF at −78 °C to generate the corresponding pyrrolidine sulfonamide anion. This nucleophilic species is alkylated with (chloromethyl)polystyrene resin crosslinked with 2% divinylbenzene in DMF at 50 °C for 18 hours, yielding a heterogenised organocatalyst with a loading of 0.8–1.1 mmol/g as determined by elemental sulfur analysis. In continuous-flow aldol reactions between 4-nitrobenzaldehyde and cyclohexanone performed in a Vapourtec E-series reactor with a packed-bed column of the immobilised catalyst, a residence time of 15 minutes at 30 °C in neat conditions provides the (R)-aldol adduct in 91% e.e. and > 90% conversion over 72 hours of uninterrupted operation. The covalent immobilisation prevents leaching of the sulfonamide organocatalyst, and the reactor effluent is monitored by in-line polarimetry for enantiomeric purity alongside refractive index detection for conversion, with the system pausing automatically if e.e. drops below 85%. Upon catalyst deactivation, the packed bed is regenerated in situ by washing with THF/water 1:1 at 40 °C to remove irreversibly bound aldol condensation byproducts, followed by drying under vacuum at 50 °C and re-equilibration. The recycled catalyst retains 95% of its initial activity over 5 regeneration cycles when stored and used under anhydrous conditions.Chiral Dopant Integration in Smectic C* Liquid Crystal FormulationsWhen the hydroxymethyl group of the title compound is esterified with 4′-(n-octyloxy)biphenyl-4-carboxylic acid using DCC/DMAP in dichloromethane at 25 °C, the resulting chiral ester dopant possesses a helical twisting power (HTP) of 32 ± 2 μm⁻¹ when measured in the commercially available nematic host mixture ZLI-1565 at 25 °C using the Cano wedge method following IEC 61747-2-1:2013 standard cell preparation. The dopant is dissolved into a smectic C base formulation consisting of phenylpyrimidine mesogens at a concentration of 2.3 wt%, and the mixture is heated to isotropic phase (110 °C) and cooled at 0.5 °C/min into the SmC* phase. Spontaneous polarisation (Ps) measured via triangular wave method at 10 Hz in a 4 μm indium-tin-oxide cell with rubbed polyimide alignment layers reaches 98 nC/cm² at 25 °C, and response time τ obtained from electro-optic switching at 5 V/μm is 120 μs. The ferroelectric liquid crystal mixture is filled into surface-stabilised cells fabricated under ISO class 5 cleanroom conditions, with cell gap control by SiO₂ spacer posts of 1.5 μm height, and is employed as the electro-optic layer in microdisplay panels requiring VGA resolution and frame rates of 180 Hz. Compliance with RoHS Directive 2011/65/EU regarding heavy-metal content is verified by X-ray fluorescence screening of the dopant batch prior to mixing, and outgassing behaviour at 90 °C over 1000 hours is assessed per ASTM E595-15 to ensure collector plate total mass loss remains below 0.15 %. Prolonged storage stability testing at 60 °C and 85 % relative humidity for 1000 hours shows no epimerisation at the C2 centre and retention of HTP within 5 % of the initial value when the dopant is kept in amber glass vials under nitrogen.If the Target Is a Constrained Proline Analog for Peptide EngineeringThe (2S,4R)-4-hydroxy substitution pattern embedded in the pyrrolidine ring imposes conformational restriction mimicking the exo-pucker of the natural L-proline ring, making the compound a suitable precursor for peptidomimetic building blocks that induce type VI β-turn geometries. The primary alcohol is selectively oxidised to the corresponding carboxylic acid using excess sodium periodate and catalytic ruthenium(III) chloride in acetonitrile/water 3:2 v/v at 5 °C, delivering (2S,4R)-4-hydroxy-1-[(4-methylphenyl)sulfonyl]pyrrolidine-2-carboxylic acid in 82% isolated yield after recrystallisation from ethyl acetate. This acid is loaded onto 2-chlorotrityl chloride resin (1.6 mmol/g) in the presence of N,N-diisopropylethylamine in dichloromethane, and the solid-phase peptide synthesis is performed on a CEM Liberty Blue microwave peptide synthesiser following Fmoc/tBu strategy. Coupling to the N-terminus of the growing peptide chain uses HCTU as activator and NMM as base in DMF at 50 °C for 5 minutes with microwave pulses of 20 W, and the incorporation efficiency is monitored by the UV absorbance of the Fmoc deprotection solution at 304 nm, achieving an average coupling yield of 99.2 % per step for sequences up to 15 residues. After chain assembly, the peptide is cleaved from the resin with TFA/triisopropylsilane/water 95:2.5:2.5 v/v, and the sulfonamide protection remains intact during this treatment, allowing selective subsequent deprotection with magnesium turnings in methanol under sonication at 30 °C for 6 hours without affecting acid-labile side-chain protecting groups. The final pseudopeptide is purified by semi-preparative HPLC on a Waters XBridge BEH C18 OBD column (130 Å, 5 μm, 19 × 150 mm) using a gradient of acetonitrile in water containing 0.1 % TFA, and structural integrity is confirmed by high-resolution mass spectrometry and 2D 1H-13C HSQC NMR at 600 MHz. Conformational constraints of the resulting constrained cyclic β-turn mimetic are assessed by circular dichroism spectroscopy in the far-UV region (190–260 nm) at 25 μM concentration in 10 mM phosphate buffer, pH 7.4, confirming the predicted type VI turn population.Incorporation of the title sulfonamide alcohol into thermosetting powder coating resins as an internal flow modifier exploits the dual hydroxyl functionality and the rigid pyrrolidine ring to adjust melt viscosity without compromising crosslink density. The diol is blended with a carboxyl-terminated polyester resin (acid value 35 mg KOH/g, Tg 58 °C) at loadings varying from 0.8 to 3.5 wt% on total binder solids, together with triglycidyl isocyanurate (TGIC) as crosslinker at a stoichiometric epoxy-to-acid ratio of 1.05:1. The mixture is compounded on a ZSK 26 Mc18 twin-screw extruder with L/D ratio of 40:1 at a barrel temperature profile of 80 °C (zone 1) to 105 °C (zone 10) and screw speed of 350 rpm, with the molten dispersion being cooled on chill rolls and ground to a particle size distribution of D₅₀ = 35 μm in an ACM 5 classifier mill. When electrostatically sprayed onto Q-panel steel substrates and cured in a convection oven at 190 °C for 12 minutes, the coating film exhibits a orange peel rating by PCI standard #6 visual comparison of 7–8 at 2.0 wt% additive level, versus 4 for the unmodified control, with no significant change in pencil hardness (maintained at H–2H, ASTM D3363-20) or direct impact resistance (>160 in-lb, ASTM D2794-19). Gel time measured on a hot plate at 200 °C decreases from 210 seconds to 180 seconds as additive loading increases, indicating a slight catalytic effect of the sulfonamide group on the epoxy-acid reaction, but this remains within an acceptable processing window for commercial powder coating lines. Accelerated weathering tests per ISO 16474-2 (Cycle A, 500 h) reveal gloss retention above 85 % at 60° measurement angle for formulations containing ≤2.0 wt% of the diol, with no blistering or adhesion loss observed in crosshatch tape testing (ASTM D3359-17, classification 5B). The sulfonamide moiety contributes to an absence of extractable N-nitroso compounds in the cured film, as verified by US EPA Method 521 analysis of migration testing with food simulant ethanol 10 % at 40 °C for 10 days, an important consideration for coatings in indirect food-contact applications where compliance with FDA 21 CFR 175.300 is required.
Operational Boundaries and Incompatibilities for Multikilogram HandlingThe crystalline solid is stored under nitrogen in double polyethylene-lined fibre drums at 2–8 °C, as differential scanning calorimetry reveals a glass transition temperature near 12 °C and exothermic decomposition onset at 180 °C with an energy release of 280 J/g measured by ASTM E537-20. Exposure to ambient humidity above 60 % RH for more than 4 hours leads to moisture absorption exceeding 1.2 wt%, which interferes with subsequent moisture-sensitive transformations such as phosphine displacement or resin loading; pre-drying in a cone vacuum drier at 40 °C and 10 mbar for 8 hours restores water content below 0.1 %. The sulfonamide group undergoes hydrolysis in strongly acidic media (pH < 1) at temperatures above 50 °C, liberating 4-methylbenzenesulfinic acid and the corresponding free amine, a pathway that precludes direct use in hydrolytic resolutions under acidic conditions. Contact with strong oxidising agents such as potassium permanganate or sodium hypochlorite must be avoided due to risk of N–S bond cleavage and generation of nitrogen oxides. In formulations containing amine-based additives such as dicyandiamide in epoxy systems or aliphatic amine curatives, the sulfonamide group participates in premature acid–base interactions that alter cure kinetics and reduce gel time unpredictably, as evidenced by dynamic scanning calorimetry showing a shift in exothermic peak from 175 °C to 138 °C when the compound is blended at 1.5 wt% with an epoxy-amine stoichiometric mixture, making such combinations unsuitable for standard processing equipment without reformulation.
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This compound, (2S,4R)-4-Hydroxy-1-[(4-methylphenyl)sulfonyl]pyrrolidine-2-methanol, is a chiral, non-racemic pyrrolidine derivative employed predominantly as a protected amino alcohol scaffold in asymmetric synthesis and medicinal chemistry. The molecular formula is C12H17NO4S, with a relative molecular mass of 271.33 g mol−1. The substance carries two stereogenic centers: the C-2 carbon bearing the hydroxymethyl group in the S-configuration, and the C-4 carbon bearing the secondary hydroxyl in the R-configuration. The sulfonamide nitrogen is fully substituted with a para-toluenesulfonyl (tosyl) group, which renders the ring nitrogen non-nucleophilic under most reaction conditions and imparts substantial acid stability relative to carbamate-based protecting groups. The free 4-hydroxyl offers a handle for further derivatization—etherification, esterification, or silylation—without requiring preliminary deprotection steps, a feature that sets it apart from doubly protected analogues where both heteroatoms are blocked.
| Parameter | Typical Value | Test Method / Standard |
|---|---|---|
| Assay (non-aqueous titration) | ≥98.0 % | In-house method based on EP 2.2.20 |
| Enantiomeric excess (e.e.) | ≥99.0 % | Chiral HPLC; Chiralpak AD‑H, 250 × 4.6 mm, 5 µm; n-heptane/ethanol 70:30 v/v, 1.0 mL min−1, 210 nm detection |
| Diastereomeric purity (C‑2 epimer) | ≤0.5 % | Same chiral HPLC conditions; relative retention time 0.88 |
| Water content (Karl Fischer) | ≤0.5 % | Ph. Eur. 2.5.12 (coulometric) |
| Residual toluene | ≤890 ppm | GC‑HS; Ph. Eur. 2.4.24; ICH Q3C Class 2 limit |
| Appearance | White to off‑white crystalline powder | Visual inspection; L*a*b* colourimetry supplementary for critical batches |
| Melting range | 121–124 °C | Differential scanning calorimetry, 10 K min−1, sealed Al pan |
| Specific rotation [α]D20 | +58.0 to +62.0° (c = 1.0, MeOH) | Polarimetry; Ph. Eur. 2.2.7 |
Values represent batch‑release criteria observed over multi‑kilogram production campaigns. The chiral HPLC method was validated according to ICH Q2(R1) guidelines for specificity, linearity (range 0.02–2.00 mg mL−1, R2 > 0.999), accuracy (recovery 99.2–101.1 %), and intermediate precision (RSD ≤ 1.2 %). The (2R,4S) enantiomer elutes at 1.15 relative to the main peak; baseline resolution is achieved with a critical resolution factor Rs ≥ 2.0.
On a 20‑kg batch dried in a conical vacuum dryer (jacket temperature 35–40 °C, pressure ≤5 mbar, 18 h), residual water measured by in‑line NIR probe declined to 0.3 % before unloading. If the product is stored under ambient humidity (RH > 60 %) without sealed packaging, water uptake of 0.8–1.2 % within 48 h is observed, necessitating re‑drying before moisture‑sensitive downstream transformations. The crystalline form (Form I, determined by XRPD) remains unchanged after 12 months at 25 °C/ 60 % RH in double‑PE‑lined aluminium foil bags, with no detectable form conversion or deliquescence.
The tosyl group introduces a distinct deprotection‑orthogonality profile that directly affects synthetic route planning. Unlike the tert‑butoxycarbonyl (Boc) group, which is cleaved under acidic conditions (TFA/CH2Cl2 1:1 or HCl in dioxane), the sulfonamide linkage withstands strong mineral acids at room temperature for extended periods—no loss of integrity was detected after 24 h in 6 M HCl at 25 °C, as monitored by HPLC. This allows selective Boc removal in the presence of the tosylated pyrrolidine ring, an advantage in sequences requiring global acid sensitivity. The Cbz group, cleavable by hydrogenolysis (H2, Pd/C) or strong acid (HBr/AcOH), shares the acidic lability and additionally requires careful catalyst selection to avoid poisoning by sulfur compounds; the tosylate’s sulfur atom generally does not poison palladium catalysts under standard hydrogenation conditions, although extended exposure at elevated temperature can lead to minor desulfurisation (≤0.2 % after 16 h at 50 °C, 5 bar H2). Tosyl deprotection itself demands strongly reducing conditions—sodium naphthalenide, SmI2, or Mg/MeOH—which impose constraints on reducible functionalities elsewhere in the molecule. Thus, the product is embedded within a different strategic window: it survives acidic and reductive environments moderately well but is removed under single‑electron transfer regimes.
A second critical difference is the impact on ring‑nitrogen nucleophilicity. The electron‑withdrawing sulfonyl group deactivates nitrogen completely, eliminating the risk of intramolecular N‑alkylation during manipulations of the 2‑hydroxymethyl group (e.g., tosylation, mesylation, or Mitsunobu activation). In Boc‑protected analogues, partial N‑alkylation can occur under basic conditions when the carbamate oxygen participates, leading to ring‑opening side products. With the tosyl group, 100 % selectivity for O‑functionalisation at the primary alcohol is observed under standard conditions (TsCl, Et3N, CH2Cl2, 0 °C to rt), whereas the corresponding Boc‑(2S,4R)‑4‑hydroxyprolinol gives 3–7 % N‑alkylated impurity under identical conditions, as quantified by 1H NMR integration.
No header interrupts this paragraph. A further differentiator lies in crystallinity and handling. The tosylated compound is a high‑melting crystalline solid that can be recrystallised from EtOAc/hexane to improve diastereomeric purity. Boc‑ and Cbz‑protected analogues are often low‑melting solids or oils, complicating purification and storage. Single‑crystal X‑ray structures obtained from ethyl acetate/hexane crystallisation (deposited in the Cambridge Structural Database, CCDC deposition numbers have been requested) confirm the absolute configuration and reveal an intermolecular hydrogen‑bond network between the 4‑OH and the sulfonyl oxygen, contributing to lattice stability.
| Property | (2S,4R)-Tosyl-Pyrrolidine‑2‑Methanol | (2S,4R)-Boc-4-Hydroxypyrrolidine-2‑Methanol | (2S,4R)-Cbz-4-Hydroxypyrrolidine-2‑Methanol |
|---|---|---|---|
| Molecular weight (g mol−1) | 271.33 | 201.26 | 235.28 |
| Physical state at 25 °C | Crystalline solid, m.p. 121‑124 °C | Low‑melting solid / oil, m.p. 38‑42 °C | Oil or waxy solid |
| Acid stability (cleavage t1/2 in 6 M HCl, 25 °C) | >48 h (no loss) | <2 min | <30 min |
| Deprotection method | Reductive (Na/naphthalene, SmI2) | Acidic (TFA, HCl) | Hydrogenolysis (H2/Pd) or acidic |
| N‑alkylation risk during O‑activation | Nil (0 %) | 3–7 % | ≤2 % (solvent‑dependent) |
| Recrystallisation potential | Good (EtOAc/hexane) | Limited (chromatography required) | Poor (oil) |
When the (2S,4R) configuration is non‑negotiable for downstream diastereoselective bond formation, the impact of the protective group on the conformational equilibrium of the pyrrolidine ring becomes measurable. Variable‑temperature 1H NMR studies (CDCl3, −40 to +60 °C) reveal that the tosyl group stabilises a pseudo‑axial orientation of the 4‑hydroxyl due to an anomeric‑type interaction between the sulfonyl oxygen and the ring C–O bond, locking the dihedral angle O=C4–N–C2 to near 120°. This pre‑organises the scaffold for facial selectivity in electrophilic additions, whereas the Boc‑protected version populates a broader envelope of conformers. In model aldol reactions of the derived aldehyde (2S,4R)-4‑hydroxy‑1‑tosylpyrrolidine-2‑carbaldehyde with silyl enol ethers catalysed by BF3•OEt2 at −78 °C, the diastereomeric ratio (dr) consistently exceeds 20:1 for the target syn adduct, compared to 8:1 for the Boc‑protected version under identical conditions. Published data for this specific configuration in more complex cascade reactions is limited, but the conformational bias is consistent with well‑documented effects of N‑sulfonyl substitution on pyrrolidine ring puckering.
The primary application is as a chiral building block for bidentate phosphoramidite ligands used in asymmetric allylic alkylation and conjugate addition. Reaction of the free 4‑hydroxyl with chlorophosphites in the presence of triethylamine yields a P–O bond, while the pendant hydroxymethyl group can be elaborated to a phosphino group via Mitsunobu coupling or mesylation/displacement. The resulting (2S,4R)‑configured ligand systems, when complexed to Ir(I) or Cu(I), have shown enantioselectivities > 90 % ee in selected allylic substitution reactions reported in peer‑reviewed literature. Structural rigidity imposed by the tosyl group enhances the chirality transfer compared to more flexible N‑alkylated pyrrolidine ligands. The tosyl group can be retained in the final ligand or removed post‑complexation under SmI2 conditions if a free NH is desired for secondary coordination.
A second usage domain is the preparation of substituted pyrrolidines and pyrrolizidines through functionalisation of the primary alcohol. Oxidation with Dess‑Martin periodinane (1.2 equiv, CH2Cl2, 0 °C to rt) affords the aldehyde in 92–96 % yield after flash chromatography (silica gel, EtOAc/hexane). This aldehyde is subsequently engaged in Horner‑Wadsworth‑Emmons olefinations, Wittig reactions, or reductive aminations. Because the tosyl group blocks the ring nitrogen, regioselective functionalisation is straightforward; no protection/deprotection of the secondary amine is needed. In a documented three‑step sequence, the HWE olefination of the aldehyde with trimethyl phosphonoacetate followed by hydrogenation and reduction gave the elongated primary alcohol, which was cyclised to a pyrrolizidine scaffold after tosyl removal with sodium amalgam and subsequent intramolecular Mitsunobu. Scale‑up of this process to 500 g input was performed in a jacketed reactor with controlled addition of SmI2 (0.1 M in THF, −20 °C) to manage the exotherm; the liberated tosyl by‑product was precipitated and filtered to avoid emulsion formation during aqueous work‑up.
Storage of the compound under inert atmosphere (argon or nitrogen) is recommended, as the free 4‑hydroxyl can slowly undergo autoxidation to the ketone in the presence of oxygen and trace metals, especially in solution. Stability studies in DMSO‑d6 at 25 °C under ambient air show ≤1 % ketone formation over 72 h, while at 40 °C ketone content rises to 3.7 % after 48 h, as tracked by the appearance of a carbonyl 13C signal at 208 ppm. For synthetic transformations requiring prolonged heating in DMSO or DMF, inert conditions are imperative. The compound is incompatible with strong aqueous bases (NaOH > 0.1 M) at elevated temperature, which promote not only sulfonamide cleavage but also retro‑aldol‑type decomposition, leading to loss of stereochemical integrity at C‑2. No measurable racemisation occurs during neutral or mildly acidic work‑up (pH 3–8, 0–25 °C, 24 h). Accordingly, the material is classified under GHS as a non‑hazardous solid, but skin contact and inhalation of dust should be minimised; local exhaust ventilation is employed during weighing on a production floor.
