--- title: "Evans aldol reaction Template – Chemistry Diagram | MolDraw" url: https://www.moldraw.com/templates/evans-aldol/ description: "Evans aldol reaction template: Bu₂BOTf and Hünig’s base turn (S)-4-benzyl-3-propionyloxazolidin-2-one into its Z-boron enolate; benzaldehyde adds through a…" 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/) › Evans aldol reaction [Name reactions](https://www.moldraw.com/templates/name-reactions/)Premium # Evans aldol reaction template ![Evans aldol reaction template: Bu₂BOTf and Hünig’s base turn (S)-4-benzyl-3-propionyloxazolidin-2-one into its Z-boron enolate; benzaldehyde adds through a chair transition state to give the (2S,3S) syn aldol with high diastereoselectivity.](https://www.moldraw.com/templates/evans-aldol.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). Bu₂BOTf and Hünig’s base turn (S)-4-benzyl-3-propionyloxazolidin-2-one into its Z-boron enolate; benzaldehyde adds through a chair transition state to give the (2S,3S) syn aldol with high diastereoselectivity. ## Mechanism step by step A Z-boron enolate of an oxazolidinone imide reacts through a Zimmerman–Traxler chair: the “Evans syn” aldol 1. **Boron triflate binds** – The imide C=O oxygen displaces triflate from Bu₂BOTf 2. **Z-enolate** – Hünig’s base removes the α-H: the Z-boron enolate (OBBu₂ and CH₃ cis) 3. **Aldol through the chair** – Six atoms (B, O, C, C, C, O) in a chair: the C–C bond forms as the aldehyde O binds boron (see the chair below) ## Key points - Zimmerman–Traxler: a chair-like six-membered transition state; the Z-enolate puts its CH₃ and the aldehyde R both pseudo-equatorial, so Z → syn (an E-enolate would give anti). - Bu₂BOTf with a hindered amine gives the Z-boron enolate; short B–O bonds make the chair tight, so boron aldols are more selective than lithium aldols. - Face selection: the oxazolidinone C=O points away from the enolate C–O (dipoles opposed) and the benzyl group blocks one face, giving the “Evans syn” isomer (dr typically > 99 : 1). - The auxiliary is removed afterwards (LiOH/H₂O₂ → acid, LiBH₄ → alcohol) and recovered. Drawn with 155 atoms, 12 arrows, 38 shapes – every one editable in MolDraw. ## Sources - [Clayden, Greeves & Warren, Organic Chemistry, 2nd ed., OUP 2012, ch. 33](https://openlibrary.org/isbn/9780199270293) Textbook - [Clayden, Greeves & Warren, Organic Chemistry, 2nd ed., OUP 2012, ch. 41](https://openlibrary.org/isbn/9780199270293) Textbook - [Kürti & Czakó, Strategic Applications of Named Reactions in Organic Synthesis, Elsevier 2005](https://openlibrary.org/isbn/9780124297852) 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 Evans aldol reaction template free? You can preview the Evans aldol reaction 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 Evans aldol reaction 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? 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