Nitrogen carbonyl derivatives

Carbonyldiimidazole does certainly stand out as one of the most remarkable reagents for peptide coupling. Carboxylic acids react readily with this reagent to yield acyl imidazoles which in turn couple with the amino group of a peptide to produce a new acyl-nitrogen linkage with very little racemization. Reaction of the acylimidazolide with other nucleophiles can lead to a variety of carbonyl derivatives (62AG(E)35l). 

Our consideration of rearrangements to electron-deficient heteroatoms must be brief. In discussing migrations to electron-deficient nitrogen, we first discuss three rearrangements that occur in carbonyl derivatives, the Beckmann, Hofmann, and Schmidt rearrangements, and then consider rearrangements of nitrenium ions. 

Ylides based upon sulfur are the most generally useful in these cyclopropane-forming reactions.133 Early work in this area was done with the simple dimethyloxysulfonium methylide (9) derived from dimethyl sulfoxide. The even simpler dimethylsulfonium methylide (10) was studied at the same time as a reagent primarily for the conversion of carbonyl compounds into epoxides.134 Somewhat later, other types of sulfur ylides were developed, among which the nitrogen-substituted derivatives such as (11) are... 

REACTIONS OF METAL CARBONYLS AND METAL CARBONYL DERIVATIVES WITH THE MULTIDENTATE NITROGEN LIGANDS blpy, phen, AND terpy... 

Unlike cobalt and rhodium, the chemistry of polynuclear iridium carbonyl derivatives has not been studied in detail (15a). Reduction of Ir4(CO)i2 under carbon monoxide with K2C03 in methanol gives the yellow tetranuclear hydride derivative [Ir4(CO)nH], whereas under nitrogen the brown dianion [Ir8(CO)2o]2- has been isolated as a tetraalkylam-monium salt (97). It has been suggested that the structure of the dianion could result from the linking of two iridium tetrahedra, although its formulation so far is based only on elemental analyses. Clearly such an interesting compound deserves further chemical and structural characterization. 

Nitrogen-containing derivatives of carbonyl compounds are prone to facile oxidation by DIB. Under the proper conditions a geat variety of substrates afforded different types of products, as illustrated in Table 3.4. 

Acylation-reduction converts ammonia to a primary amine, a primary amine to a secondary amine, or a secondary amine to a tertiary amine. These reactions are quite general, with one restriction The added alkyl group is always 1° because the carbon bonded to nitrogen is derived from the carbonyl group of the amide, reduced to a methylene (—CH2—) group. 

It may be clear that this reaction involves the formation of one C-C and one C-0 bond during the linking of three molecules I, II, and methanol from the solvent. The combination of an expectedly strong electrophile such as the pyrrolinium ion (I) and a very mild nucleophile represented here by isopropylene, falls within the familiar framework of a Prins -type reaction. That process has a protonated form of a carbonyl derivative as the electrophile, usually an aldehyde of which the iminium ion would be a nitrogen homolog. However, in contrast with the classical Prins reaction whereby 1,3-dioxanes result by the inclusion of a second mole of the electrophile, in the present reaction 1 mol of methanol is incorporated instead. 

Usually decarboxylation is accomplished by heating the acids above their melting points, often in the presence of a copper-chromium catalyst. Imidazole-4,5-dicarboxylic acid can be monodecarboxylated by heating its monoanilide imidazole- and benzimidazole-2-carboxylic acids decarboxylate very readily indeed, so readily that the carboxyl function makes a useful blocking group in metallation procedures (see Scheme 7.2.1) [3-5]. A potentially useful method of preparation of imidazole-4-carboxylic acid derivatives heats the 4,5-dicarboxylic acid (2) with acetic anhydride to form (1), which is essentially an azolide and very prone to nucleophilic attack which cleaves the nitrogen-carbonyl bond (Scheme 8.3.1). With methanol the methyl ester (3) is formed with hydrazines the 4-hydrazides (4) result [6]. 

Naphthalene-catalyzed lithiation of l,3-dimethyl-2-phenylimidazolidine leads to cleavage of the benzylic carbon-nitrogen bond, with formation of an intermediate dianion. The dianion could be trapped with several electrophiles, including primary and secondary alkyl halides, as well as enolizable and nonenolizable carbonyl derivatives, affording diamines 485 in satisfactory yields (Scheme 112) <2005T3177>. 

Compound classes, not previously described (eg. 5- and 6-membered heteroarenes) Compound classes, for which, in the meantime, significant improvements and progresses have been made, for example carbonic acid derivatives, carboxylic acids and carboxylic acid derivatives, aldehydes, carbonyl derivatives, halogen compounds, peroxides, sulfur, selenium, tellurium, nitrogen and phosphorus compounds. 

In this chapter the reduction of compounds with a carbon-nitrogen double bond is discussed besides the classic carbonyl derivatives, such as Schiff bases, hydrazones, and oximes, diazoalkanes are also treated. 

Iminium salts (2) can commonly be prepared from the reaction of amines with aldehydes or ketones (1 Scheme 1). With formaldehyde as the carbonyl precursor, Eschweiler-Clark-type methylation reactions may occur when using reducing acids such as formic acid. Alternatively, other sp -type, nitrogen-free carbonyl derivatives (3), such as acetals and hemiacetals, can be used, where this is favorable. Highly electron-poor carbonyls, such as chloral (c/. Scheme 10), may show distinctly decreased reactivity in aqueous solution, due to the extended hydrate formation. 

Other sp -type, nitrogen-containing carbonyl derivatives (6), such as a-amino alcohols, " a-amino ethers" e.g. oxazolidines ), a-amino sulfides e.g. thiazolidines ) and a-amino nitriles, are efficient sources for iminium ions (Scheme 3). 

Quinoline Two condensed aromatic rings in which one CH unit is replaced by a nitrogen atom. Quinone The ortho- orpara-d carbonyl derivative of cyclohexadiene. Also known as benzoquinone. 

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