Preparation of aldehydes/ketones

Alkenes are cleaved to carbonyl compounds by ozonolysis This reaction IS useful both for synthesis (preparation of aldehydes ketones or car boxyhc acids) and analysis When applied to analysis the carbonyl com pounds are isolated and identified allowing the substituents attached to the double bond to be deduced... 

The addition of lithium and Grignard reagents to isocyanides which do not contain a-hydrogens proceeds by an a-addition to produce a metalloaldimine (7, an acyl anion equivalent). The lithium aldimines are versatile reagents which can be used as precursors for the preparation of aldehydes, ketones, a-hy-droxy ketones, a-keto acids, a- and 3-hydroxy acids, silyl ketones and a-amino acids (Scheme 5). - ... 

Ozonolysis is widely used both in degradation work to locate the position of double bonds and in synthesis for the preparation of aldehydes, ketones, and carboxylic acids. Ozone is a 1,3-dipole and undergoes 1,3-dipolar cycloadditions with alkenes. 

The heterocyclic systems of 1,3-oxazinium ions are widely used in the organic synthesis . Thus, 5,6-dihydro-4/f-l,3-oxazines 40, being a cyclic derivative of 1,2-aminoalcohols, can serve as Cj-synthones for the preparation of aldehydes, ketones and carboxylic acids . The 47/-l,3-oxazines 47 can undergo oxidative dehydrogenation by treatment with the trityl salts or benzoquinone to form the 3-azapyrylium salts 48, which then give various jV-acylenamine derivatives 49-52 by reaction with water or with active methylene comjKJunds (equation 18) . 

Epoxides are reactive, versatile intermediates in organic chemistry [1,2], The epoxidation of olefins and subsequent rearrangement in the presence of acidic or basic catalysts is widely used for the preparation of aldehydes, ketones, ethers, or alcohols. The reactions are used for the synthesis of a variety of fine chemicals and are conventionally catalyzed with homogeneous catalysts such as metal halides or mineral acids. Substitution of these homogeneous systems by heterogeneous catalysts is, however, becoming increasingly attractive because they are readily separated from the product and do not usually cause environmental problems. 

This reaction has wide application in the preparation of aldehydes, ketones, lactones, quinones, and quinoxalines. 

TABLE 5 Preparation of aldehydes, ketones and alcohols during alkenes ozonolyis with consecutive reduction. 

Ozonolysis has both synthetic and analytical applications m organic chemistry In synthesis ozonolysis of alkenes provides a method for the preparation of aldehydes and ketones... 

The oxidation of alcohols by treatment of their corresponding chloroform-ates with DMSO and triethylamine has been reported by Barton. Preliminary results indicate this to be a useful method for preparation of aldehydes but cyclic secondary alcohols are converted to ketones in relatively low yields. 

While the Friedel-Crafts acylation is a general method for the preparation of aryl ketones, and of wide scope, there is no equivalently versatile reaction for the preparation of aryl aldehydes. There are various formylation procedures known, each of limited scope. In addition to the reactions outlined above, there is the Vdsmeier reaction, the Reimer-Tiemann reaction, and the Rieche formylation reaction The latter is the reaction of aromatic compounds with 1,1-dichloromethyl ether as formylating agent in the presence of a Lewis acid catalyst. This procedure has recently gained much importance. 

The reaction is an important step in a method for the oxidative decyanation of nitriles containing an a hydrogen. The nitrile is first converted to the a-hydro-peroxy nitrile by treatment with base at — 78°C followed by O2. The hydroperoxy nitrile is then reduced to the cyanohydrin, which is cleaved (the reverse of 16-51) to the corresponding ketone. The method is not successful for the preparation of aldehydes (R =H). 

Preparation of Aldehydes and Ketones from Thio- and Selenoethers... 

The general mechanistic features of the aldol addition and condensation reactions of aldehydes and ketones were discussed in Section 7.7 of Part A, where these general mechanisms can be reviewed. That mechanistic discussion pertains to reactions occurring in hydroxylic solvents and under thermodynamic control. These conditions are useful for the preparation of aldehyde dimers (aldols) and certain a,(3-unsaturated aldehydes and ketones. For example, the mixed condensation of aromatic aldehydes with aliphatic aldehydes and ketones is often done under these conditions. The conjugation in the (3-aryl enones provides a driving force for the elimination step. 

CPv. / Ti Al Tebbe reagent methylenation of aldehydes, ketones, esters, thioesters, amides, carbonates can also induce olefin metathesis in situ preparation [711-713]... 

The present procedure is a general method for the preparation of monoalkylated ketones from enamines of aldehydes and ketones with electrophilic olefins. There are many advantages in this method of alkylation. Only monoalkylation occurs, even when such reactive species as acrylonitrile are used and, when a cyclic ketone like 2-methylcyclohexanone is used, reaction occurs only at the lesser substituted center. In a general base-catalyzed reaction, substitution occurs on the more substituted center. 

Following the initial isolation of the Hnl from M. esculenta [33] in which the peptide sequence was established, an overexpressed version of this enzyme (in E. coli) was prepared [41]. This system is not limited for enzyme quantity (as outlined in Sect. 2.3), and can accept a wide range of aromatic, heterocyclic and aliphatic aldehydes, as well as ketones, as substrates. In practical terms, a measure of the degree of enzyme inhibition by substrates is of significant value and for this system this has been quantified for a range of aldehydes, ketones and alcohols [70]. It was deduced that ketones and alcohols are competitive inhibitors, whilst aldehydes are noncompetitive inhibitors. 

IPreparation of Mldehydes Some important methods for the preparation of aldehydes and Ketones and ketones are as follows ... 

Other procedures for a oxidation of ketones are based on prior generation of the enolate. The most useful oxidant in these procedures is a molybdenum compound, MoOs-pyridine-HMPA, which is prepared by dissolving M0O3 in hydrogen peroxide, followed by addition of HMPA. This reagent oxidizes the enolates of aldehydes, ketones, esters, and lactones to the corresponding a-hydroxy compound.189 190 191... 

However, the most important methods for preparing alcohols are catalytic hydrogenation (H2/Pd-C) or metal hydride (NaBH4 or LiAlH4) reduction of aldehydes, ketones, carboxylic acids, acid chlorides and esters (see Sections 5.7.15 and 5.7.16), and nucleophilic addition of organometalhc reagents (RLi and RMgX) to aldehydes, ketones, acid chlorides and esters (see Sections 5.3.2 and 5.5.5). 

Addition of water to alkynes preparation of aldehydes and ketones... 

Hydroboration-oxidation of alkynes preparation of aldehydes and ketones Hydroboration-oxidation of terminal alkynes gives syn addition of water across the triple bond. The reaction is regioselective and follows anti-Markovnikov addition. Terminal alkynes are converted to aldehydes, and all other alkynes are converted to ketones. A sterically hindered dialkylborane must be used to prevent the addition of two borane molecules. A vinyl borane is produced with anU-Markovnikov orientation, which is oxidized by basic hydrogen peroxide to an enol. This enol tautomerizes readily to the more stable keto form. 

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