enolization

This temporary appendix will in a later stage prevent unwanted enolization.

The existence of hydrogen atom at alpha carbon is necessary but not sufficient condition for enolization to occur.

This reaction produces 2-oxogulonolactone which spontaneously undergoes enolization to form ascorbic acid.

This is very common in enolization reactions and can be viewed in the figure below under "Acidic Conditions."

Enolization and trapping with triflate group.

Tertiary selenoxides, which are unable to undergo enolization, do not react further with selenium electrophiles.

Z-enolates, leading to syn-aldol adducts, can be reliably formed using boron-mediated soft enolization:

When this requirement is not enforced, for example in the adamantanone or other polycyclic ketones, the enolization is impossible or very slow.

In cases where an enolization is occurring around an allylic group (usually as part of a cyclic system), A strain can cause the reaction to be nearly impossible.

LDA is not commonly used in the classic Claisen or Dieckmann condensations due to enolization of the electrophilic ester.

The apparent shortcoming for enolate alkylation reactions is over-alkylation, even if the amount of base added for enolization as well as the reaction temperature are carefully controlled.

Soft enolization with the Lewis acid dibutulboron triflate and the base diisopropylethylamine gives the (Z)-enolate, which undergoes a diastereoselective aldol reaction with an aldehyde substrate.

The iminium hydroxide ion caused enolization of the side chain methyl ketone would be followed by ring closure to the above shown optically active bicyclic ketol product (see Figure 1.)

In the latter case, the stabilized carbonyl compound is deprotonated with a strong base (hard enolization) or with a Lewis acid and a weak base (soft enolization).

This same enolization occurs much more rapidly under basic conditions, as the carboxylic group is retained in the transition state and allows the molecule to adopt a conformation that does not cause allylic strain.

In the syn-selective reactions, both enolization methods give the Z enolate, as expected; however, the stereochemical outcome of the reaction is controlled by the methyl stereocenter, rather than the chirality of the oxazolidinone.

Use of Hydrogen Isotope Effects to Identify the Attacking Nucleophile in the Enolization of Ketones Catalyzed by Acetic Acid C. Gardner Swain, Edward C. Stivers, Joseph F. Reuwer, Jr.