Cycloadditions reaction summary

In the [2+4] pencyclic cycloaddition reaction known as the Diels-Alder reaction, fluonne-containing compounds have been widely used as dienes, dieno-philes, or both Much of the fundamental work, including many comprehensive and systematic studies, was done before 1972, and Hudlicky provides an exeellent summary of this work [9] Additional sources for early work in this area are reviews in Organic Reactions [61] and Fluorine Chemistry Reviews [62]... 

Summary N-Silylation is a crucial prerequisite for the synthesis of interesting nonnatural amino acids via cycloaddition reactions of unsaturated amines. 

Summary The formation, reactivity, and cycloaddition behavior of neopentylsilenes towards suitable reaction partners is described. Especially l,l-dichloro-2-neopentylsilene. Cl2Si=CHCH2Bu (2) - easily obtained from vinyltrichlorosilane and LiBu - is a useful building block for the synthesis of SiC four membered ring compounds. These can be converted into the isomeric Diels-Alder and retro ene products upon thermolysis reactions. The mode of the silenes cycloaddition reactions ([4+2] vs [2+2] addition) can be directed by either the substitution pattern at the Si=C moiety, the choice of reaction partners or the conditions. Furthermore the products resulting from cycloaddition reactions open up a wide variety of following reactions, which possibly will lead to new organosilicon materials or pharmaceutical compounds. 

In summary, the cycloaddition reactions of 1,2-dihydropyridines have proven to be very useful in the total synthesis of natural products. The primary reasons for their utility are that they have electron-rich reactive 7r-systems, they contain a heterocyclic nitrogen atom for alkaloid synthesis, and the stereochemistry is controlled in their cycloaddition reactions. 

In summary then we see that Kochi s work provides a direct experimental link between reactivity and reactant excited state energies. While at the present time the only excited state that has been correlated in this way is the charge transfer state, the CM model predicts that similar correlations for additional excited states are likely to exist. The significance of Kochi s work in relation to cycloaddition reactions is discussed on p. 176. 

In the following we discuss a few of these cycloadditions. A summary of these reactions by Sauer and Sustmann is soon to be published. 

In summary, the construction of phosphetane or arsetane rings is usually carried out by McBride synthesis or alkylation-cyclization methods. These methods are quite useful, with a good selectivity in most cases. [2+2] Cycloaddition reactions are also available, but this method is limited to particular cases. In addition to these methods, other useful methods based on the transformation from another ring system have been developed. These methodologies are described in Section 2.10.10. 

In summary, it is clear that silver possesses unique abilities to activate both olefinic species and small strained rings for [2+2] cycloaddition reactions. Nevertheless, reports of silver-mediated [2+2] cycloadditions remain rare. 

Summary Cl2Si=CHCH2/Bu is a versatile building block in organosilicon synthesis which reacts with a wide variety of multiple bond systems. The unique reactivity is shown by the predominance of [2+2] over [4+2] cycloaddition reactions. This unusual behaviour is caused by the two chlorine substituents at the silicon atom. This presentation shows the synthesis of silacyclobutenes from Cl2Si=CHCH2tBu and disubstituted alkynes and some chemistry of these four membered ring compotmds. 

Summary The reaction between in situ formed l,l-dichloro-2-neopentylsilene, Cl2Si=CHCH2tBu (3), and 1,1-dimethylpentaftilvene (8) leads to the formation of exo/endo-isomeric [4+2] cycloadducts 9 and [2+2] stereoisomers 10 in good yields. 2D-NMR spectroscopic investigations on the product mixture prove die different mode of the silene cycloaddition reactions ([4+2] vs [2+2] addition). 

This chapter reviews thermal [2 + 2] cycloadditions of alkenes to form cyclobutanes, extending the coverage provided by earlier summaries of the literature.It docs not deal with [2 + 2] cycloadditions that are achieved photochemically, or that utilize allenes, arynes or ketenes, or that are deliberately catalyzed, or that result in heterocyclic four-membered rings, even though these other varieties of [2 + 2] cycloaddition reactions are important and of substantial interest. 

Summary The reaction of trichlorosilane with DABCO provides the anion SiCb, which can be used instead of SiCh in cycloaddition reactions. In the presence of the 1,4-diaza-l,3-butadienes la-g, the five membered rings 2a-g are found. 2b was characterized by an X-ray structure determination. 

In summary, ZnCl2 and the lanthanide catalysts give products derived from a classical [4 + 2] cycloaddition reaction. The side chain on the aldehyde occupies an endo position in the transition state, leading to cis (endo) products. This is probably due to the large steric bulk of the solvated metal complex, which binds anti to the aldehyde side chain. In addition, vinylogous ortho ester products, which are the expected products for a cycloaddition process, can be isolated when using these catalysts. MgBr2 also... 

The Diels-Alder reaction with inverse electron demand has been one of the most intensively studied reactions of 1,2,4-triazines. In this reaction 1,2,4-triazines behave as electron-deficient dienes and react with electron-rich dienophiles to give, generally, pyridines (see Houben-Weyl, Vol. E7b, p 471 ff). [4 + 2] Cycloadditions of 1,2,4-triazines have been observed with alkenes, alkynes, strained double bonds, electron-rich double and triple bonds, but in a few cases also with electron-deficient alkynes C—N double and triple bonds can also be used as dienophiles. In addition to intermolecular Diels-Alder reactions, intramolecular [4 + 2] cycloaddition reactions of 1,2,4-triazines have also been studied and used for the synthesis of condensed heterocyclic systems. A review on the intermolecular Diels-Alder reaction was published by Boger and Weinreb 14 Sauer published a review on his studies in 1992,381 and E. C. Taylor published a summary of his own work on intramolecular Diels-Alder reactions in 1988.382... 

Cycloaddition reactions continue to find application in the synthesis of natural products and related substances containing indole and carbazole rings. Moody has published a summary of syntheses of carbazole alkaloids in which cycloadditions of pyrano[3,4-b]indol-3-ones figure prominently. <94SL681>... 

REVIEW This volume is highly recommended to all those who want to stay abreast of developments In the mechanisms and synthetic applications of 1,3-dipolar cycloaddition reactions. The writers have realized a good balance between the summary of achievements and the reporting of gaps in understanding or remaining synthetic challenges. The articles are well written, they are amply illustrated with equations or schemes. ... 

In summary, alkyl azides react with aryl isocyanates, acyl isocyanates, carboalkoxy isocyanates and sulfonyl isocyanates to afford the corresponding 1,4-disubstituted A -tetrazohne-5-ones. In contrast, the cycloaddition reaction of aryl azides to isocyanates is hmited to sulfonyl isocyanates, leading to l-aryl-4-sulfonyl-A -tetrazohne-5-ones. 

Summary Monoaminosilylenes and bis(diethylamino)silylene are formed by thermolysis of amino-substituted disilanes and characterized by trapping with dienes. In the case of MeSiNMe2, cycloaddition reactions were extended to 1,4-diheterodienes, unsaturated ketones and imines allowing an easy synthetic access to functionally substituted unsaturated silicon heterocycles. The syntheses of an isolable, unsymmetric diaminosilylene and of related germylenes and stannylenes are described. The results are presented and discussed in relation to theoretical work on stabilization of donor-substituted silylenes and recent work on isolable diaminosilylenes done by or in cooperation with other groups. 

In summary, dihydrooxadiazines were efficiently prepared by the hetero [4+2] cycloaddition reaction of azodicarboxylates and glycals. These dihydrooxadiazines can be converted to 2-amino saccharides. This method is presently being extended to the synthesis of 2-amino C-glycosides and results will be reported in a forthcoming paper. 

Scheme 3 Summary of photo-triggered cycloaddition reactions useful in biological applications, a Reactions between aUcenes and photochemically generated 1,3-dipoles or 1,3-ienes. b SPAAC between photoprotected cyclooctynes and azides...

In summary, we have accomplished the first asynunetric total synthesis of crinipellin A along with the formal total synthesis of crinipellin B. The very unique tetraquinane core structure of crinipellins was constructed efficiently through a tandem cycloaddition reaction via TMM diyl. The absolute stereochemistry of crinipellins was also confirmed through our asymmetric total synthesis. 

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