Carbonyl compounds common classes

Diaziridines, discovered in 1958, six years after the oxaziridines, were almost immediately realized to be structural analogs of oxaziridines. Like these they showed oxidizing properties unexpected for other classes of organic nitrogen compound. Properties in common with oxaziridines include the rearrangement to open chain isomers on heating above 100 °C (for several diaziridines), and their hydrolytic behavior in acidic media, which leads to carbonyl compounds with conservation of the hetero-hetero bond. 

Two classes of charged radicals derived from ketones have been well studied. Ketyls are radical anions formed by one-electron reduction of carbonyl compounds. The formation of the benzophenone radical anion by reduction with sodium metal is an example. This radical anion is deep blue in color and is veiy reactive toward both oxygen and protons. Many detailed studies on the structure and spectral properties of this and related radical anions have been carried out. A common chemical reaction of the ketyl radicals is coupling to form a diamagnetic dianion. This occurs reversibly for simple aromatic ketyls. The dimerization is promoted by protonation of one or both of the ketyls because the electrostatic repulsion is then removed. The coupling process leads to reductive dimerization of carbonyl compounds, a reaction that will be discussed in detail in Section 5.5.3 of Part B. 

Allyl- and vinylsilane chemistry was one of the first areas of reagent synthesis impacted by CM methodology. Allylsilanes are commonly employed in nucleophilic additions to carbonyl compounds, epoxides, and Michael acceptors (the Sakurai reaction) vinylsilanes are useful reagents for palladium-coupling reactions. As the ubiquitous application of CM to this substrate class has recently been described in several excellent reviews, this topic will not be discussed in detail, with the exception of the use of silane moieties to direct CM stereoselectivity (previously discussed in Section 11.06.3.2). 

Oxazolidines are an important class of compounds commonly prepared by reaction of an amino alcohol with a carbonyl compound. The reaction of an imine with an epoxide has recently been shown to efficiently provide the oxazolidine ring system <07SL646>. The reaction is catalyzed by Yb(OTf)3 and generally provides the product oxazolidine in good yield albeit with poor ( 2 1) diastereoselectivity. 

Chemistry involving transformations of the cyclopentadienyl (Cp) ligand itself will be discussed in Chapter 7 however, much of the chemistry of cyclopentadienyl complexes involves the ligand acting purely as a spectator. Thus there arises a broad area of chemistry involving complexes with both carbonyl and cyclopentadienyl ligands. The most common classes of such compounds (Table 3.4) are the mononuclear complexes... 

Whereas discrete low oxidation state compounds of the transition metals are common in organometallic chemistry, the most typical series of examples being the transition metal carbonyl compounds see Carbonyl Compound), there are at present significantly fewer classes of compounds containing main group elements in low oxidation states. An... 

Examples of photoreactions may be found among nearly all classes of organic compounds. From a synthetic point of view a classification by chromo-phore into the photochemistry of carbonyl compounds, enones, alkenes, aromatic compounds, etc., or by reaction type into photochemical oxidations and reductions, eliminations, additions, substitutions, etc., might be useful. However, photoreactions of quite different compounds can be based on a common reaction mechanism, and often the same theoretical model can be used to describe different reactions. Thus, theoretical arguments may imply a rather different classification, based, for instance, on the type of excited-state minimum responsible for the reaction, on the number and arrangement of centers in the reaction complex, or on the number of active orbitals per center. (Cf. Michl and BonaCid-Kouteck, 1990.)... 

Treatment of test solutions with specific reagents in combination with the phase-equilibrium method for functional group identification of volatile impurities in aqueous solutions is common [19—23]. The analysis is based on the interaction of a definite class of substances with the selected reagents in the liquid phase with the formation of involatile derivatives, accompanied by the disappearance of the corresponding peaks in the chromatogram of the equilibrium gas phase above the solution (e.g., carbonyl compounds are removed on treatment of the test solution with hydroxylammonium chloride, sulphides with mercury(II) chloride and ethers and carbonyls with basic hydroxylamine... 

Some examples of the addition of one carbonyl compound to another are the aldol condensation the formation of acetoacetic ester the condensation of benzaldehyde with one of the components of a mixture of an acid anhydride and a carboxylate salt the formation of mesityl oxide, phoroiie, and mesitylene from acetone and the condensations of aromatic aldehydes and ketones. Acids and bases are generally catalysts for these reactions. They have sufficient in common to warrant their being classed together as the aldol type of... 

It is rather more common to use enamines or silyl enol ethers in acylations with acid chlorides. These are more general methods—enamines work well for aldehydes and ketones while silyl enol ethers work for all classes of carbonyl compounds. It is possible to combine two enolizable molecules quite specifically by these methods, and we shall consider them next. 

Although several classes of carbonyl compounds or their derivatives react with allylboronates (see below), the most common use of allylboronates in synthetic chemistry is their nucleophilic addition to aldehydes to produce secondary homoallylic alcohols (Figure 6.5) [1-6], a process first discovered in 1974 [lOj. 

Carbonyl halides are a common class of compounds, especially for cases where the metal center is in an odd oxidation state. An example of such a compound is ReX(CO)s (X = Cl, Br, I) from which luminescence is observed at 25 From an analysis of the electronic spectra of this complex the lowest energy absorption bands have been attributed to the ligand field transitions (e hal)... 

Other common classes of compounds which, according to the linking theory, possess carbonyl groups, are carboxylic acids, esters, amides, acyl halides, etc. These groups, however, do not exhibit the typical carbonyl condensation reactions. 

In this chapter, we begin to study the reactions functional groups that contain a carbonyl group (C=0). The simplest of these is formaldehyde a model that shows the dipole and electron distribution is shown on the left. The high polarity of the carbonyl group dominates the chemistry of carbonyl compounds. Functional groups that contain a carbonyl group include aldehydes, ketones, carboxylic acids, and their derivatives, and many classes of cellular molecules. These compounds have some common chemistry, but there are many variations. We will discuss carbonyl compounds in Chapters 18-22. 

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