Esters Enolates Aldol

What is an enolate

Negatively charged ion formed by deprotonating alpha hydrogen on ketone

Is the alpha-hydrogen acidic/basic/neutral

Acidic

Why is the alpha hydrogen acidic

Resonance stabilization of the anion

Is an enolate electrphilic/nucleophilic/neutral

Nucleophilic

Thermodynamic vs Kinetic enolate

Thermodynamic: More stable, forms more substituted alkene

Kinetic: Forms faster, forms less substituted alkene

Reagent for Thermodyanmic enolate

Small base, warm

Reagents for kinetic enolate

Bulky base, cold

Reaction 1: Alkylation

SN2

Deliver an R group to alpha carbon

Alkylation reagents

1. Strong base (NaH, LDA)

2. RX

Reaction 2: Aldol Condensation

Aldehyde/Ketone + Aldehyde/Ketone

Alkoxide Intermediate (O-)

Aldol Addition Intermediate (After PT on O-. beta-hydroxy-carbonyl)

Poor LG leaves

Aldol Condensation reaction pattern

Enolate stays same (loses proton)

Electrophilie loses C=O

Crossed Aldol condensation

Guaranteed enolate (one molecule has no alpha hydrogens)

Examples of molecules that lack alpha protons (for crossed aldol)

Formaldehyde, Benzaldehyde

Intramolecular aldol

2 C=O in same molecule,

Alpha carbon deprotonated, attack other C=O