--- title: "Fischer indole synthesis Template – Chemistry Diagram | MolDraw" url: https://www.moldraw.com/templates/fischer-indole-synthesis/ description: "Fischer indole synthesis template: Acetone phenylhydrazone tautomerises to the ene-hydrazine. After N-protonation a [3,3]-sigmatropic shift makes the new C–C…" lang: en publisher: Scidart Academy generated: 2026-11-13 --- [MolDraw](https://www.moldraw.com/) › [Templates](https://www.moldraw.com/templates/) › [Name reactions](https://www.moldraw.com/templates/name-reactions/) › Fischer indole synthesis [Name reactions](https://www.moldraw.com/templates/name-reactions/)Premium # Fischer indole synthesis template ![Fischer indole synthesis template: Acetone phenylhydrazone tautomerises to the ene-hydrazine. After N-protonation a [3,3]-sigmatropic shift makes the new C–C bond and breaks the N–N bond; rearomatisation, attack of the aniline nitrogen on the iminium ion and loss of ammonia give 2-methylindole.](https://www.moldraw.com/templates/fischer-indole-synthesis.webp) [Edit in MolDraw](https://www.moldraw.com/)Download with Pro Premium template. Preview and edit it free in MolDraw; downloading and exporting it is part of [MolDraw Pro](https://www.moldraw.com/pricing). Acetone phenylhydrazone tautomerises to the ene-hydrazine. After N-protonation a [3,3]-sigmatropic shift makes the new C–C bond and breaks the N–N bond; rearomatisation, attack of the aniline nitrogen on the iminium ion and loss of ammonia give 2-methylindole. ## Mechanism step by step An aryl hydrazone and acid give an indole: [3,3] shift, ring closure, loss of NH₃ 1. **Phenylhydrazone** – Condensation with the ketone (acid catalysed) 2. **Ene-hydrazine** – Acid-catalysed tautomerisation, like imine → enamine 3. **N-Protonation** – The N next to the alkene takes a proton 4. **[3,3]-Sigmatropic shift** – Key step: the new C–C bond forms as the weak N–N bond breaks 5. **Rearomatisation** – Tautomerisation (C–H → N–H) restores the benzene ring 6. **Ring closure** – The aniline N attacks the iminium carbon: a cyclic aminal 7. **Proton transfer** – H⁺ moves from the ring N to NH₂, making NH₃⁺ a good leaving group 8. **Loss of NH₃** – The ring N lone pair pushes out ammonia 9. **Deprotonation** – Loss of a C–H proton gives the aromatic indole ## Key points - Accepted mechanism (Robinson): ene-hydrazine, [3,3]-sigmatropic shift, ring closure, loss of NH₃; ¹⁵N labelling shows the N next to the ketone carbon is the one lost. - The ketone needs an α-CH₂ or CH₃; unsymmetrical ketones can give two indoles, depending on which ene-hydrazine forms. Cyclohexanone gives tetrahydrocarbazole. - Brønsted (H₂SO₄, AcOH, PPA) or Lewis acids (ZnCl₂, BF₃) catalyse it; acetaldehyde fails, so indole itself is made another way. - Used for tryptamines and the triptan anti-migraine drugs (e.g. sumatriptan). Drawn with 227 atoms, 22 arrows, 15 shapes – every one editable in MolDraw. ## Sources - [Kürti & Czakó, Strategic Applications of Named Reactions in Organic Synthesis, Elsevier 2005, Fischer indole synthesis](https://openlibrary.org/isbn/9780124297852) Textbook - [Clayden, Greeves & Warren, Organic Chemistry, 2nd ed., OUP 2012, ch. 30](https://openlibrary.org/isbn/9780199270293) Textbook ## How to use this template 1. Press **Edit in MolDraw**. The template opens on the canvas of the free MolDraw editor. 2. Change anything: move structures, edit atoms and labels, recolour highlights or delete what you do not need. 3. Add your own structures, arrows and text next to it, or combine several templates on one page. 4. Export the drawing as PNG, SVG or PDF for slides, worksheets, theses and papers. ## Frequently asked questions ### Is the Fischer indole synthesis template free? You can preview the Fischer indole synthesis template here and open and edit it in MolDraw for free. Downloading or exporting it is part of MolDraw Pro, together with the other premium templates. ### Can I edit the Fischer indole synthesis template? Yes. It opens as an ordinary MolDraw drawing, so every structure, arrow, label and colour can be changed, and you can add your own content around it. ### Is the chemistry checked? Every structure is checked with RDKit and every curly arrow passes MolDraw’s electron-flow audit. The sources used are listed on this page. ### Which name reactions are included? Over seventy, covering the reactions most often asked in school-leaving exams (A-level, IB, CBSE, JEE and NEET) and first-year university courses, including condensations, rearrangements, oxidations, reductions and aromatic substitutions. ## More name reactions templates [**Fischer esterification**Free · Name reactions](https://www.moldraw.com/templates/fischer-esterification/)[**Grignard addition to a ketone**Free · Name reactions](https://www.moldraw.com/templates/grignard-addition/)[**Michael addition**Free · Name reactions](https://www.moldraw.com/templates/michael-addition/)[**Diels–Alder reaction**Premium · Name reactions](https://www.moldraw.com/templates/diels-alder/)[**Friedel–Crafts acylation**Premium · Name reactions](https://www.moldraw.com/templates/friedel-crafts-acylation/)[**Claisen condensation**Premium · Name reactions](https://www.moldraw.com/templates/claisen-condensation/)[**Friedel–Crafts alkylation**Premium · Name reactions](https://www.moldraw.com/templates/friedel-crafts-alkylation/)[**Cannizzaro reaction**Premium · Name reactions](https://www.moldraw.com/templates/cannizzaro-reaction/) ## Related pages [**Curved Arrow Mechanism Worksheet**Free printable worksheet](https://www.moldraw.com/educational-materials/curved-arrow-mechanism-worksheet/)[**Predict the Product Worksheet: Organic Reactions**Free printable worksheet](https://www.moldraw.com/educational-materials/predict-the-product-worksheet/)[**All Name reactions templates**93 templates](https://www.moldraw.com/templates/name-reactions/)[**All chemistry templates**525 templates in 31 categories](https://www.moldraw.com/templates/) MolDraw Pro Download all 525 templates - Export the 437 premium templates as PNG, SVG or PDF - AI chemistry assistant - Structure scanning from images - Cloud save and teaching slides [See Pro plans](https://www.moldraw.com/pricing) Free templates stay free. 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