2c. Alkylation of aldehydes and ketones using LDA

Compounds that contain two electron withdrawing groups in a 1,3-relationship are called active hydrogen compounds or active methylene compounds. This terminology refers to the enhanced acidity of hydrogen atoms bonded to a carbon situated between two electron-withdrawing groups.

Synthesis of α-hydroxy ketones ..

Aldol products are easily recognized as b-hydroxy ketones (and b-hydroxy aldehydes):

hydroxy ketones in good yields by potassium permanganate oxidation

The ketone enolate forms easier than the ester enolate since their a-hydrogens are more acidic. Thus, the ketone will act as the nucleophile and the ester will behave as the electrophile.

Hydroxy ketone synthesis by oxidation - Organic …

Esters must have at least two a-hydrogen atoms to undergo the Claisen condensation; one hydrogen is removed to form the enolate, a second hydrogen is removed from the b-ketoester. The second proton abstraction is the driving force step.

Synthesis of .alpha.-siloxy epoxides and .alpha.-hydroxy carbonyl compounds,

Alpha-hydroxy ketone - WikiVisually

However, there are many exceptions to this sequence depending on the reagents used, as well as steric and electronic effects in the substrate. In addition to peracids, alkaline hydrogen peroxide or hydrogen peroxide together with a Bronsted or Lewis acid like BF3 can also be effective. The migratory tendency can be quite different with different reagents. For example, benzaldehyde gives mostly H migration with KHSO5, mostly Ph migration with H2O2/NaOH, and about equal amounts of both with MCPBA. Electron rich aryl rings migrate preferentially over electron poor ones, and thus the sequence among secondary, aryl, and hydrogen migratory aptitudes can be changed by substituents on the aromatic ring. Vinyl groups migrate comparably to aryl, but the enol ester products are often epoxidized during the reaction.

Sterol synthesis : chemical synthesis of 3 beta-hydroxy-5 alpha ..

Synthetically related to the Baeyer-Villiger oxidation is the haloform reaction, inserted here for lack of a better location. In the haloform reaction methyl ketones are cleaved to carboxylic acids by treatment with 3 equiv of bromine, chlorine or iodine in the presence of base. The reaction involves consecutive α-halogenations of the methyl group to form a trihalo-ketone, which is then cleaved in a Grob-type fragmentation.

Analogous to the mixed Aldol, this reaction works best when one ester does not have any alpha-hydrogen atoms.

Chemoenzymatic synthesis of chiral [alpha]-hydroxy ..

Photoinitiators undergo a unimolecular bond cleavage upon irradiation to yield free radicals (benzoin esters; benzil ketals; alpha-dialkoxy acetophenones; alpha-hydroxy alkylphenones; alpha-amino alkylphosphine; acylphosphine oxides).

It is formed from a condensation reaction aldehydes or ketones with hydrazines (commonly phenylhydrazine).

A domino synthesis of α-hydroxy ketones has been ..

The Baeyer-Villiger oxidation involves the peroxide-induced insertion of an oxygen between the carbonyl carbon and one of the substituents to form an ester (or a lactone if the ketone was cyclic, as in the example below) through the action of a hydroperoxy oxidant, usually a percarboxylic acid, but hydrogen peroxide itself under acid or base-catalyzed conditions will sometimes be reactive enough for aldehydes or if the ketone is strained (e.g. cyclobutanones).

Novel synthesis of .alpha.-hydroxy ketones and …

Hydrazones and hydrazines are converted to aldehydes and ketones to corresponding hydrocarbons by heating the carbonyl compound with sodium ethoxide (Wolf-Kishner reduction).