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Enols and enolate formation (fundamentals)

21 real reactions from the literature: keto–enol tautomerization on enols, phenols and aryl ketones; silyl enol ether formation on six-membered cyclic ketones, five-membered cyclic ketones and methyl ketones; and more. Each scheme shows starting materials, conditions and products, with the yield and reference where the source reports them.

Printable worksheets (PDF): Keto-Enol Tautomerization: examples; Enolate Formation: with or without products.

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  1. Keto–enol tautomerization: hydroxy-1-cyclohexene-1-carboxylic acid (an enol) with H2O gives 2-oxocyclohexanecarboxylic acid (the tautomer).
    Keto–enol tautomerizationJ. Am. Chem. Soc. 2003, 125, 6478

  2. Silyl enol ether formation: 2-hydroxycyclohexan-1-one (a six-membered cyclic ketone) with 1) 2 eq LiTMP; 2) 2 eq TMSCl gives 1,2-bistrimethylsilyloxy cyclohexene (the silyl enol ether) and 1,2-bis(trimethylsilyloxy)-2-cyclohexene (the silyl enol ether). 15% yield.
    Silyl enol ether formationRealOChem worksheet

  3. Kinetic enolate formation: 2-methylcyclohexanone (a six-membered cyclic ketone) with LDA, DME; − 40-0 °C gives lithium 6-methylcyclohexen-1-olate (the kinetic enolate).
    Kinetic enolate formationOrg. Synth. Coll. Vol. 6, p. 121

  4. Alkene isomerization: 3-cyclohexen-1-one (a six-membered cycloalkene) with NaOH; NaOH gives 2-cyclohexen-1-one (the α,β-unsaturated ketone).
    Alkene isomerizationRealOChem worksheet

  5. Enamine formation: cyclohexanone (a six-membered cyclic ketone) with p-TsOH, toluene, Δ gives 4-(cyclohexen-1-yl)morpholine (the enamine).
    Enamine formationOrg. Synth. Coll. Vol. 5, p. 808

  6. Enol ester formation: isopropenyl acetate (an enol ester) and methyl 1-oxo-2,3-dihydro-1H-indene-2-carboxylate (a β-keto ester) with thermodynamic gives methyl 3-(acetyloxy)-1H-indene-2-carboxylate (the enol ester).
    Enol ester formationRealOChem worksheet

  7. Thermodynamic enolate formation: 2-methylcyclohexanone (a six-membered cyclic ketone) with 1) 1.05 eq KH / RT; 2) add BEt3; 1) 1.05 eq KN(SiMe3)2 -78 C; 2) add BEt3 gives the thermodynamic enolate.
    Thermodynamic enolate formationTetrahedron Lett. 1983, 24, 1341

  8. Imine–enamine tautomerization: an enamine gives the tautomer.
    Imine–enamine tautomerizationJ. Am. Chem. Soc. 1964, 86, 4283

  9. Lactam–lactim tautomerization: 1-(4-methyl-6-oxo-1H-pyrimidin-2-yl)-3-pentylurea gives 1-(4-methyl-6-oxo-1H-pyrimidin-2-yl)-3-pentylurea (the lactim tautomer).
    Lactam–lactim tautomerizationJ. Am. Chem. Soc. 2005, 127, 810

  10. Keto–enol tautomerization: 1,4-naphthalenediol (a phenol) with TFA gives 2,3-dihydro-1,4-naphthoquinone (the tautomer).
    Keto–enol tautomerizationAngew. Chem. Int. Ed. 2006, 45, 98

  11. Silyl enol ether formation: 2-hydroxycyclohexan-1-one (a six-membered cyclic ketone) with excess Et3N / TMSCl, reflux gives 1,2-bistrimethylsilyloxy cyclohexene (the silyl enol ether) and 1,2-bis(trimethylsilyloxy)-2-cyclohexene (the silyl enol ether). 67% yield.
    Silyl enol ether formationRealOChem worksheet

  12. Kinetic enolate formation: 2-(1,3-benzodioxol-5-yl)cyclohexan-1-one (a six-membered cyclic ketone) with LDA, -78 C gives the kinetic enolate.
    Kinetic enolate formationJ. Org. Chem. 2005, 70, 6523

  13. Alkene isomerization: 5-methylcyclopent-2-en-1-one (an α,β-unsaturated ketone) with NaOH (2 equiv) gives 2-methyl-2-cyclopenten-1-one (the α,β-unsaturated ketone).
    Alkene isomerizationRealOChem worksheet

  14. Enamine formation: cyclooctanone (an eight-membered cyclic ketone) with p-TsOH, xylene; D gives 1-[(1E)-cycloocten-1-yl]pyrrolidine (the enamine).
    Enamine formationOrg. Synth. Coll. Vol. 5, p. 277

  15. Enol ester formation: 2-pent-2-ynylcyclopentan-1-one (a five-membered cyclic ketone) with thermodynamic; temp; temp = 100 C; 50% gives (2-pent-2-ynylcyclopenten-1-yl) acetate (the enol ester) and the enol ester.
    Enol ester formationRealOChem worksheet

  16. Silyl enol ether formation: methyl 3-oxopyrrolidine-1-carboxylate (a five-membered cyclic ketone) with Method A: 1.1 eq LDA -78 C then TMSCl (50%); Method B: 0.8 eq variant (63%) gives the silyl enol ether and the silyl enol ether. 50-63% yield.
    Silyl enol ether formationRealOChem worksheet

  17. Silyl enol ether formation: 1-[benzyl(methyl)amino]propan-2-one (a methyl ketone) with Method A: ketone to 1.1 eq LDA at -78 C then TMSCl (kinetic, 75%); Method B: 0.8 eq variant (thermodynamic) gives the silyl enol ether and the silyl enol ether.
    Silyl enol ether formationRealOChem worksheet

  18. Thermodynamic enolate formation: 2-(1,3-benzodioxol-5-yl)cyclohexan-1-one (a six-membered cyclic ketone) with 1) Et3N, TMSCl; 2) MeLi gives the thermodynamic enolate.
    Thermodynamic enolate formationJ. Org. Chem. 2005, 70, 6523

  19. Keto–enol tautomerization: an enol with MeOH; 65 °C gives the tautomer. 68% yield.
    Keto–enol tautomerizationJ. Am. Chem. Soc. 1968, 90, 1367

  20. Keto–enol tautomerization: anthrone (an aryl ketone) with AcOH gives anthranol (the tautomer).
    Keto–enol tautomerizationJ. Chem. Soc., Perkin Trans. 2 2002, 784

  21. Kinetic enolate formation: 2-methylcyclohexanone (a six-membered cyclic ketone) with 1) 1.05 eq KN(SiMe3)2, -78 C; 2) add BEt3 gives the kinetic enolate.
    Kinetic enolate formationTetrahedron Lett. 1983, 24, 1341