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Otherwise, the most acidic carbonyls are typically also the most active electrophiles: first aldehydes, then ketones, then esters, and finally amides. Thus cross-aldehyde reactions are typically most challenging because they can polymerize easily or react unselectively to give a statistical mixture of products. [16]
The intramolecular reaction was not reported until 1991 [5] but has become important in the synthesis of natural products. [6] The reaction is effective with carboxylic acids to give amines (above), and with ketones to give amides (below).
For these latter reactions, two equivalents of the incoming group add to form an alcohol rather than a ketone or aldehyde. This occurs even if the equivalents of nucleophile are closely controlled. Overaddition of nucleophiles. The Weinreb–Nahm amide has since been adopted into regular use by organic chemists as a dependable method for the ...
Since, aldehydes reduce more easily than ketones, they require milder reagents and milder conditions. At the other extreme, carboxylic acids, amides, and esters are poorly electrophilic and require strong reducing agents. [17] The idealized equation for the reduction of a ketone by sodium borohydride is: 4 RCOR' + NaBH 4 → NaB(OCHRR') 4
[4] [5] The reaction has since been extended to the synthesis of β-keto esters from the condensation between aldehydes and diazo esters. [6] The general reaction scheme is as follows: General Scheme for Buchner Reaction. The reaction yields two possible carbonyl compounds (I and II) along with an epoxide (III). The ratio of the products is ...
Wittig reactions are most commonly used to convert aldehydes and ketones to alkenes. [1] [2] [3] Most often, the Wittig reaction is used to introduce a methylene group using methylenetriphenylphosphorane (Ph 3 P=CH 2). Using this reagent, even a sterically hindered ketone such as camphor can be converted to its methylene derivative.
Many types of carbonyl compounds, including aldehydes, ketones, esters, thioesters, carboxylic acids, and amides, can be converted into enolate ions by reaction with LDA. Note that nitriles, too, are acidic and can be converted into enolate-like anions (referred to as nitrile anions).
The Norrish type I reaction is the photochemical cleavage or homolysis of aldehydes and ketones into two free radical intermediates (α-scission). The carbonyl group accepts a photon and is excited to a photochemical singlet state. Through intersystem crossing the triplet state can be obtained.