Cycloadditions nitrogen-containing compounds

Azides are useful intermediates for synthesis of various nitrogen-containing compounds. They undergo cycloaddition reactions, as will be discussed in Section 6.2,... 

Another type of reaction that has been developed in order to resolve nitrogen-containing compounds is the Diels-Alder cycloaddition. As a rare example, Sibi et al. [235] have recently reported the KR of pyrazohdinones that could not be obtained in high enantioselectivities from direct methods on the basis of a Diels-Alder cycloaddition with cyclopentadiene catalysed by a combination of Cu(OTf)2 with a chiral aminoindanol-derived bisoxazohne hgand. The recovered almost enantiopure (98% ee) substrate was isolated with a selectivity factor of 34. Excellent results were also reported by Fu et al. [236] for the KR of azomethine imines via copper-catalysed [3-1-2] cycloadditions with aUcynes performed in the presence of a chiral phosphaferrocene-oxazoline ligand, which furnished the chiral recovered substrates with high selectivity factors of up to 76, as shown in Scheme 3.15. 

Intramolecular cycloadditions of o-quinodimethanes (144), generated thermally from (145), are useful in the preparation of some polycyclic nitrogen-containing compounds, e.g. (146). ... 

Azides are useful intermediates for synthesis of various nitrogen-containing compounds. They undergo cycloaddition reactions, as will be discussed in Section 6.2, and can also be easily reduced to primary amines. Azido groups are usually introduced into aliphatic compounds by nucleophilic substitution. The most reliable procedures involve heating the appropriate halide with sodium azide in DMSO or DMF. Alkyl azides can also be prepared by reaction in high-boiling alcohols ... 

The synthesis of nitrogen containing heterocyclic systems by photocylo-addition processes is virtually limited to examples involving [ 2 + 2] cycloaddition of imines, nitriles, and azo compounds. Successful additions are few in number and the requirements for success uncertain. The reactions do not proceed with the facility with which carbonyl containing compounds undergo photocycloaddition to alkenes to give oxetans, and various explanations have been advanced to account for this observed lack of reactivity.226... 

Nitrogen-containing heteroaromatic compounds react with (chloromethyl)[(tri-methylsilyl)methyl] sulfide in the presence of CsF to afford fused 1,3-thiazolidines of type 130. These compounds are the result of a formal [3 + 2] cycloaddition of the parent thiocarbonyl ylide la across the C=N bond (170). In these cases, the formation of the five-membered cycloadduct is believed to occur in two steps via an intermediate onium ion. 

A completely different, important type of synthesis, which was developed more recently, takes advantage of the electrophilicity of nitrogen-containing 1,3-dipolar compounds rather than the nucleophilicity of amines or enamines. Such compounds add to multiple bonds, e.g. C—C, C C, C—O, in a [2 + 3 -cycloaddition to form five-membered heterocycles. 

A similar reaction, with functionalities reorganized, may also be used to form tricyclic compounds. Thus, sulfonylimines (as part of a diene system) react by [4+2] intramolecular cycloaddition with an appropriately placed alkene moiety as shown in equation 191689. Some aromatization of the nitrogen-containing ring also occurs. This problem of a mixed product can be overcome by treating the reaction mixture with DBU/DDQ, which gives the aromatized product in 84% yield. 

This reactivity of N-acylenamines 1 has opened up new possibilities for the use of enamides. in photochemical rearrangements2 as well as in acid-catalyzed cyclizations3,4, which lead to a variety of complex nitrogen-containing heterocycles from readily available simple precursors. These reactions have also been used to form a wide variety of natural products and polyfunctional compounds. Enamides can be also used as electrophilic reagents for amidoalkylation5,6, which can occur under certain conditions as a [4 + 2] cycloaddition to form 1,3-oxazinium heterocycles7. 

Photochemical reactions of nitrogen-containing thiocarbonyl compounds ([2 + 2] cycloaddition to alkenes with formation of thietanes, transformations of thioimides to lactams and cyclic amines, cyclizations of thioamides) 03H(59)399. 

Organic azido compounds react with alkene, ketone, X=Y triple bonds, X=Y double bonds, and alkyne to generate cycloaddition products— five-membered nitrogen-containing heterocyclic compounds. Under heating or catalysts, organic... 

Cycloadditions of azido compounds and various functional groups are a classic synthesis of triazoles with nitrogen containing rings. Their intramolecular cycloadditions derive a lot of organic compounds. Lukina et al. [14] synthesized... 

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