Aldehydes reaction with esters

Methylpyrazine reacts with sodamide in liquid ammonia to generate the anion, which may be alkylated to give higher alkylpyrazines (Scheme 10) (61JOC3379). The alkylpyrazines have found extensive use as fiavouring and aroma agents (see Section 2.14.4). Condensation reactions with esters, aldehydes and ketones are common, e.g. methyl benzoate yields phenacylpyrazine in 95% yield, and reactions of this type are summarized in Scheme 11. 

CpjZrClj, Zn, CHjBrj, THF methylenation of aldehydes, ketones no reaction with esters [714]... 

In the case of the benzothiazole system, both aldehydes and mixed ketones have been synthesized by reduction or alkylation of the appropriate carbonyl precursors. The carbonyl compounds are in turn prepared from the benzothiazole-2-anion either directly by reaction with esters or indirectly by reaction with aldehydes followed by PCC oxidation (Scheme 154) (85H2467 91BCJ3256). 

Phosphoranes and phosphonate derived carbanions are also known to react with carbonyl compounds other than aldehydes and ketones, in reactions often referred to as non-classical Wittig reactions.35 Wittig olefination products can be obtained from the reaction of esters, anhydrides and some amides and imides with a range of stabilized and reactive phosphoranes. The reaction of stabilized and semi-stabilized phosphoranes with esters gives alkenes (Scheme 7). However, non-stabilized phosphoranes, such as methylenetriphenylphosphorane, tend to give P-keto phosphoranes on reaction with esters (Scheme 7)—the careful choice of the reaction conditions can also permit the preparation of the alkene in these reactions. 

This constitution of the hydrate is indicated by the fact that it does not give the aldehyde reaction with fuchsine as does both acet-aldehyde and chloral. Also by the fact that the ethyl ester of such a di-hydroxy alcohol is known and is formed from chloral by reaction with alcohol. 

Claisen condensation. A condensation reaction discovered in 1890 in which aldehydes react with esters of the type RCH2COOR in the presence of metallic sodium or sodium ethylate to form unsaturated esters R"CH=C(R)COOR. The mechanism... 

Most of the a-oxygenated aldehydes in Table 19 display the characteristic trend toward (Z)-enoate formation with Ph3P=CHC02R" (2j). A simple example of this phenomenon was discussed in connection with Table 16 (2-formyltetrahydropyran entries), but a number of others had been reported much earlier (Table 19, entries 61-93) (126-127). Table 19 also includes the first systematic solvent comparisons (entries 61-67) for an a-alkoxy aldehyde reaction with an ester-stabilized ylide (126). This series of experiments represents the most dramatic known example of solvent effects on selectivity (92 8 Z E in methanol 14 86 Z E in DMF), but the results are qualitatively similar to the solvent study in Table 16. In several other examples, the isomer ratios in methanol are reported to reach synthetically useful levels (> 90%) of the (Z)-enoate (Table 19, entries 19, 20, 23-25). However, most of the methanol entries fall in the more typical range of 70-85% (Z)-enoate. No similar trend is seen with p or y-oxygenated aldehydes (Table 19, entries 102-113) that lack an a-alkoxy group. 

Several improvements in acylation techniques were announced. Butyllithium wwas determined to be superior to sodium amide in preparation of amide ions for ammonolysis reactions with esters. Phosgene is more reactive than ethyl chloroformate toward eneamines. The intermediate acyl chlorides may then be converted to a variety of products. a-Acetylenic aldehydes are easily prepared by the action of acetylenic Grignard reagents upon ethyl formate. ... 

The key step in a basealdol reaction is nucleophilic addition of the enolate anion from one carbonyl-containing molecule to the carbonyl group of another carbonyl-containing molecule to form a tetrahedral carbonyl addition intermediate. This mechanism is illustrated by the aldol reaction between two molecules of acetaldehyde. Notice that OH is a true catalyst An OH is used in Step 1, but another OH is generated in Step 3. Notice also the parallel between Step 2 of the aldol reaction and the reaction of Grignard reagents with aldehydes and ketones (Section 12.5) and the first step of their reaction with esters (Section 14.7). Each type of reaction involves the addition of a carbon nucleophile to the carbonyl carbon of another molecule. 

Secondary and tertiary alcohols can be prepared by reacting a Grignard reagent with aldehydes and ketones, respectively, but these are not the only electrophiles that can be used with a Grignard. Grignards also have useful reactions with esters and epoxides. These reactions also give alcohol products, but they lead to alternate retrosynthetic strategies for certain alcohol TMs. 

K[HSi(OEt)4] reduces aldehydes, ketones, and esters in the absence of added catalyst. Treatment of nonenolizable amides yields the corresponding aldehydes. Reaction with 1 equiv of isocyanate in diethyl ether or THF leads quantitatively to the potassium imidate, which can be quenched in situ (eq Furthermore, use of an excess of aryl isocyanate yields to the corresponding isocyanurate. ... 

As in its reactions with esters and amides, bis(2-methylpropyl)aluminum (diisobutylalumi-num) hydride (DIBAL) adds to a nitrile only once to give an imine derivative. Aqueous hydrolysis then produces an aldehyde. 

Notes The reaction is suitable for the detection of alcohols of Cs and higher. A positive reaction is also given by hydroaromatic alcohols, phenols, and all compoimds with a double bond in the chain or in the ring, as well as compounds with a three-membered ring. Some ketones (acetone, methyl ethyl ketone, cyclohexanone) and aldehydes (acetaldehyde, propionaldehyde, isovaleraldehyde) also react positively. As regards the reaction with esters of acids and glycols, the data in the literature are conflicting. 

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