Koser's reagent (HTIB)

Technical Specifications

Product Description & Scientific Applications

Koser's reagent, [hydroxy(tosyloxy)iodo]benzene or HTIB (C13H13IO4S), is a hypervalent iodine(III) oxidant carrying both a hydroxy and a tosyloxy group on the same iodine. That mixed pair is the point: the two ligands differ so widely in effective electronegativity that the reagent ionises in solution at room temperature, and tosylate is the better nucleofuge, making it more reactive than the diacetoxy analogue.

It is used as a crystalline solid, added directly to the substrate in 95% methanol at room temperature. In fluoroalcohol media — trifluoroethanol or HFIP — it switches mode, generating aromatic cation radicals by single-electron transfer. Its relatively benign character compared with thallium(III) nitrate and silver nitrate is a practical reason it displaced those oxidants.

Applications and Reactions

• Arylalkenes to α-aryl ketones: in 95% methanol, regiospecifically. The transformation the reagent is best known for.
• α-Tosyloxylation of ketones: installs a tosyloxy leaving group at the α-carbon, the first step of a two-step route to α-haloketones — and a route to the same products without handling toxic, lachrymatory α-haloketones at all.
• Heterocycles from α-tosyloxy ketones: with primary selenoamides in refluxing acetonitrile/methanol they give 1,3-selenazoles; with 3-alkyl/aryl-4-amino-5-mercapto-1,2,4-triazoles in refluxing ethanol, triazolothiadiazines in 67–93% yield.
• Oxidative aromatisation: converts Hantzsch 1,4-dihydropyridines to the corresponding pyridines in dichloromethane at room temperature, in good to excellent yields.
• Ring expansion: 1-vinylcycloalkanol derivatives to ring-expanded oxygen heterocycles in one oxidative step, 72–88% yield.
• Nitrogen deletion: with ammonium carbamate, a pyrrolidine becomes a densely substituted cyclobutane in 58% yield as a single diastereomer.
• Hofmann–Löffler–Freytag: as oxidant with 4 equivalents of sodium carbonate as bulking additive, 84% yield under mechanochemical conditions.
• Iodonium salt synthesis: dehydrative condensation with uracil in fluoroalcohol medium gives uracil-aryliodonium(III) tosylates.
• Catalytic use: with m-CPBA as terminal oxidant it is regenerated in situ, converting symmetrical dialkyl bromoalkenes to α-bromoketones in 49–54% isolated yield.
• Limitations: in sulfonyloxylation, HTIB added as the solid gave 26% against 65% for iodine(III) generated in situ — the difference is the strongly acidic medium, which activates the iodine(III) centre, so added TsOH is worth trying. In ring contraction of 1,2-dihydronaphthalenes it forms more addition by-products than thallium(III) nitrate, and some alkenes in methanol give a complex mixture.
• Storage: room temperature in a tightly sealed container, protected from light.

Shipping Destinations

• EU & UK: Priority delivery, 2–5 business days.
• United States (DDP): 3–7 business days, duties and taxes prepaid.
• EFTA Countries (DDP): 3–7 business days, duties and taxes prepaid.
• Worldwide: 7–14 business days, selected locations.