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A 1,6-Conjugate addition attacks the delta carbon of an extended conjugated electrophile. The resulting extended enolate can be protonated at different sites; proton transfer or equilibration can favor a product retaining carbonyl–alkene conjugation.

Acetone is the ketone $\mathrm{C}{\mathrm{H}}_3\mathrm{COC}{\mathrm{H}}_3$, with a carbonyl group between two methyl groups. Its polar carbonyl makes it a useful solvent and an electrophilic center for nucleophilic addition.

Hydrogens on its adjacent methyl groups can be removed to form an enolate. Thus one molecule illustrates both carbonyl electrophilicity and the carbon acidity used in carbon-carbon bond-forming reactions.

Addition of an enolate or enol to an aldehyde or ketone, giving a beta-hydroxy carbonyl compound. Subsequent dehydration is a distinct step and gives an aldol condensation.

An aldol addition followed by water elimination, commonly producing a conjugated carbonyl compound. Identifying which carbonyl supplies the enolate distinguishes constitutional products.

The aldol reaction forms a carbon-carbon bond when an enol or enolate adds to an aldehyde or ketone. The initial addition product is a beta-hydroxy carbonyl compound, containing the combined carbon frameworks.

For example, acetaldehyde can add to another acetaldehyde molecule to give 3-hydroxybutanal. Subsequent loss of water gives an alpha,beta-unsaturated carbonyl compound, the condensation product. Keeping addition and dehydration distinct explains why an aldol reaction need not itself eliminate water. The reaction is useful for constructing longer carbon skeletons with predictable functional groups.

Allyl chloroformate is $\mathrm{ClC}(\mathrm{O})\mathrm{OC}{\mathrm{H}}_2\mathrm{CH}=\mathrm{C}{\mathrm{H}}_2$. oxygen acylation of an enolate makes an allyl enol carbonate.

An ambident nucleophile can form a bond through more than one atom. An enolate can attack through carbon or oxygen; these give distinct products, although its resonance contributors describe the same ion.

An aldol addition organized through a boron enolate and a coordinated carbonyl partner. Enolate geometry and auxiliary-controlled facial selection jointly determine product stereochemistry.

Butan-2-one is the four-carbon ketone $\mathrm{C}{\mathrm{H}}_3\mathrm{C}(=\mathrm{O})\mathrm{C}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_3$. Its two sides are constitutionally different, so its two alpha positions need not react equivalently.

Formation and trapping of different enolates can give distinct substitution products. The example connects a simple molecular structure with enolate regioselectivity.

A carbon acid is a chemical acid that loses a proton from a carbon-hydrogen bond, producing a carbanion or a resonance-stabilized related species. The name refers to the atom bearing the acidic hydrogen, not to every compound containing carbon.

For example, deprotonation of acetone next to its carbonyl group gives an enolate. Delocalization of the negative charge makes this hydrogen much more acidic than an ordinary alkane hydrogen. Carbon acidity therefore explains how carbon nucleophiles arise in reactions such as the aldol reaction, while the actual acid strength depends strongly on substituents and solvent.

carbon acylation of an ester enolate followed by deprotonation of the beta-dicarbonyl product. ketone-enolate acylation by an acyl chloride is a closely related acyl-substitution strategy, although it is not the classical ester self-condensation.

Conjugate addition attacks a beta position in a conjugated electrophile and redistributes pi bonding, often generating an enolate. proton transfer then supplies a saturated carbonyl product.

An enolate is the conjugate base formed by removing an alpha proton from a suitable carbonyl compound. Oxygen-centred and carbon-centred resonance contributors help explain its ability to react at either site.

Reaction of an enolate with an acyl electrophile. carbon acylation of a ketone enolate gives a 1,3-diketone; O-acylation gives a different connectivity.

Enolate alkylation forms a carbon–carbon bond by attack of an enolate carbon on an alkyl electrophile, commonly through an SN2 reaction. Solvent, counterion, aggregation and electrophile identity affect competition with oxygen alkylation.

Preference for forming or reacting one enolate of a carbonyl compound with more than one alpha site. A less substituted kinetic enolate and an equilibrated more substituted enolate can give different carbon skeletons.

An enolate derived by deprotonation alpha to an ester carbonyl.

Finasteride is an unsaturated 4-azasteroid inhibitor of steroid 5α-reductase. Enzyme-generated reduction and enolate capture of oxidized cofactor give a covalent cofactor–inhibitor adduct; the protein itself need not be covalently modified.

Herbert G. Bull coauthored research on finasteride.^[ref]

Finasteride is an unsaturated 4-azasteroid inhibitor of steroid 5α-reductase. Enzyme-generated reduction and enolate capture of oxidized cofactor give a covalent cofactor–inhibitor adduct; the protein itself need not be covalently modified.

An aldol reaction between two reactive sites of the same molecule. A tethered enol or enolate attacks a carbonyl group to close a ring; the tether, conformation and competing chemical reactions influence the product.