Carbonyl groups addition reactions

With certain other nucleophiles addition takes place at the carbon-carbon double bond rather than at the carbonyl group Such reactions proceed via enol intermediates and are described as conjugate addition ox 1 4 addition reactions... 

Aldol Addition and Related Reactions. Procedures that involve the formation and subsequent reaction of anions derived from active methylene compounds constitute a very important and synthetically useful class of organic reactions. Perhaps the most common are those reactions in which the anion, usually called an enolate, is formed by removal of a proton from the carbon atom alpha to the carbonyl group. Addition of this enolate to another carbonyl of an aldehyde or ketone, followed by protonation, constitutes aldol addition, for example... 

Enolates can also serve as carbon nucleophiles in carbonyl addition reactions. The addition reaction of enolates with carbonyl compounds is of very broad scope and is of great synthetic importance. Essentially all of the enolates considered in Chapter 7 are capable of adding to carbonyl groups. The reaction is known as the generalized aldol addition. 

In contrast to the saturated azlactones, the Friedel-Crafts reaction of 2-substituted-4-arylidene-5-oxazolones is quite complex and may follow several different courses, often concurrently, depending on both reaction conditions and structural variations in the arylidene ring. This behavior is readily interpreted in terms of the a,)S-unsaturated carbonyl moiety and the cross-conjugated system containing nitrogen, both of which provide potential reaction sites in addition to the lactone carbonyl group. The reaction has been investigated " ... 

Acid-catalyzed hydration of isolated double bonds is also uncommon in biological pathways. More frequently, biological hydrations require that the double bond be adjacent to a carbonyl group for reaction to proceed. Fumarate, for instance, is hydrated to give malate as one step in the citric acid cycle of food metabolism. Note that the requirement for an adjacent carbonyl group in the addition of water is the same as that we saw in Section 7.1 for the elimination of water. We ll see the reason for the requirement in Section 19.13, but might note for now that the reaction is not an electrophilic addition but instead occurs... 

Carboxylic acids and esters can also be converted to amines with loss of the carbonyl group by reaction with hydrazoic acid, HN3, which is known as the Schmidt reaction,278 The mechanism is related to that of the Curtius reaction. An azido intermediate is generated by addition of hydrazoic acid to the carbonyl group. The migrating group retains its stereochemical configuration. 

The starting reagent is the Reformatsky-typt. In this case, instead of adding to a carbonyl group, addition is to the nitrile. See Reformatskv Reaction for a discussion of reagent. 

Magnesium, 235 Samarium(II) iodide, 270 Titanium(IV) chloride, 304 Addition reactions to carbonyl groups—Addition of functionalized CARBON NUCLEOPHILES (see also Aldol reaction and other specific condensation reactions, Meth-ylenation, Peterson Olefination, Refor-matsky reaction, Wittig reaction, Wittig-Horner reaction)... 

Ethynyl carbinols (propargylic alcohols) such as 134 (Scheme 2.58) represent another important group of oxidation level 3 compounds. Their preparation involves nucleophilic addition of acetylides to the carbonyl group, a reaction that is nearly universal in its scope. Elimination of water from 134 followed by hydration of the triple bond is used as a convenient protocol for the preparation of various conjugated enones 135. Easily prepared O-acylated derivatives are extremely useful electrophiles in reactions with organocuprates, which proceed with propargyl-allenyl rearrangements to furnish allene derivatives 136. 

The lone pairs may act as nucleophiles in substitution reactions of alkyl halides and sulfonates, in the solvolysis of epoxides, and in addition reactions to carbonyl groups. These reactions often proceed with acid or base catalysis. 

Enolates react with other carbonyl groups at the electrophilic carbonyl carbon. These reactions are more complicated because the initial addition adduct goes on to form different products depending on the structure of the carbonyl group. These reactions form the subject of Chapter 24. 

Introduction. The reactions of aldehydes and ketones can be conveniently divided into three groups (1) reactions involving an addition to the carbonyl group, (2) reactions involving oxidation-reduction of the carbonyl group, and (3) condensation and polymerization reactions. 

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