Cycloadditions reactions with, alkenes alkynes

Gilbert, A. (2004) 1,4-Quinone Cycloaddition Reactions with Alkenes, Alkynes, and Related Compounds, in CRC Handbook of Organic Photochemistry and Photobiology, 2nd edn (eds F. Lenci and W.M. Horspool), CRC Press, New York, pp. 87-1-87-12. 

Quinone Cycloaddition Reactions with Alkenes, Alkynes, and Related Compounds... 

Creed, D., 1,4-Quinone cycloaddition reactions with alkene, alkynes and related compounds, in CRC Handbook of Organic Photochemistry and Photobiology, Horspool, W. M. and Song, P.-S., Eds., CRC Press, Boca Raton, FL, 1995, 280. 

Other examples of the iodonium ylide-based syntheses of furan derivatives involve cycloaddition reactions with alkenes or alkynes. Although the majority of these syntheses involve stable iodonium ylides (86JOC3453 94T11541) (e.g., Eqs. 16 and 17), in some cases the ylides are unstable and are generated in situ (92JOC2135) (e.g., Eq. 18). In the case of alkenes, dihydrofuran derivatives are obtained (Eqs. 16-18). This synthetic route is especially useful for the synthesis of dihydrobenzofuran derivatives that are related to the neolignan family of natural products (Eq. 18). 

Thiobenzoyl isocyanate is widely used as a starting material for the syntheses of TAs 23-28 both in condensation with ethyl sodiocyanoacetate (86KGS3) and in [4 + 2]-cycloaddition reactions with alkenes and alkynes containing electron-donor groups (81CB2713 85ZC324) (Scheme 4). It is established that the rate of cycloaddition increases from alkenes to alkynes and with the electron-donor properties of substituents. 

Application of azomethine ylides in dipolar cycloaddition reactions with alkenes provides a route to pyrrolidine derivatives, as illustrated by the generation of the intermediate 498, and its subsequent conversion to the target system 499 (Scheme 64) <1995TL9409>. The use of alkynes as dipolarophiles instead gives rise to 3-pyrrolines, which has been exploited in a route to indoloquinones <1997JOC4763>. 

Fluorinated cyclobutenes synthesized from the cycloaddition of fluoroalkenes with non-fluorinated alkynes (vide supra) undergo pyrolysis to give fluorinated butadienes, e.g. the pyrolysis of 3,3.4,4-tetrafluorocyclobut-l-ene gives l,1,4,4-tctrafluorobuta-l,3-diene (15) almost quantitatively. Tetrafluorodienes of this type undergo [2-F 2]-cycloaddition reactions with alkenes to give fluorinated cyclobutancs. ... 

Since the initial demonstrations of the participation of substituted l,2,4,S-tetrazines ° and oxa-zoles ° ° in [4 + 2] cycloaddition reactions with alkene and alkyne dienophiles, the investigation and application of the Diels-Alder reactions of heteroaromatic systems possessing reactive azadienes have been pursued extensively. A number of general reviewshave treated the spectrum of heteroaromatic azadienes that participate in [4 + 2] cycloaddition reactions and many of the individual heteroaromatic systems have been reviewed separatcly. ° ° An extensive account was published recently and should be consulted for descriptions of the [4 + 2] cycloaddition reactions of the common heteroaromatic azadienes that have been observed to date. 

Nitrileoxidomethyl)penam sulfone, prepared in a few steps from commercially available (- -)-6-aminopenicilla-nic acid by treatment of oxime 617 with NCS and followed by dehydrochlorination with bis(tributyltin)oxide, underwent smooth 1,3-dipolar cycloaddition reactions with various alkynes, and alkenes, to give cycloadducts 618 in moderate to good yields. Some acid derivatives 618 (R = H) showed potent /3-lactamase inhibitory activity (Scheme 148) <20000L3087>. 

The most intensively studied reactions of 1,2,4,5-tetrazines are cycloaddition reactions with alkenes and alkynes, not only due to theoretical interest but also due to its importance in synthesis. The 1,2,4,5-tetrazines are diene components in this [4 + 2]-cycloaddition reaction while the alkynes and alkenes are the dienophiles. Kinetic studies have shown that these reactions should be classified as Diels Alder reactions with inverse electron demand. Therefore, 1,2,4,5-tetrazines with electron-withdrawing substituents (C02Me, CF3) and dienophiles with electron donating substituents are the most reactive compounds. However, dimethyl... 

Methyl-1,2-dihydropyridine behaves as an enamine rather than as a diene at — 10°C in its primary cycloaddition reactions with alkenes and alkynes. At higher temperatures, the [2 -I- 2] cyclo-adducts, e.g. (79), are unstable, and the more thermodynamically stable Diels-Alder endo- and exo-adducts, e.g. (80) and (81), are formed. ... 

Azomethine imines readily undergo 1,3-dipolar cycloaddition reactions with alkenes and alkynes to furnish pyrazoUdines and pyrazolines, respectively (Scheme 5.21). 

The in situ generation of nitrile oxides 119 and subsequent intra- or intermolecular 1,3-dipoIar cycloaddition reactions with alkenes and alkynes represent one of the most exploited strategies for the preparation of diverse isoxazoline 121 and isoxazole 120 derivatives. Ciufolini et al. [89] reported that PIDA in combination with a substoichiometric amount of TFA efficiently oxidize aldoximes 118 to nitrile oxides 119, which were trapped in situ with olefins to afford... 

On the whole, the cycloaddition of alkynes to nitrile N-oxides is one of the most important routes to isoxazoles, but in spite of its potentially wide application, its synthetic utility is less than that of the corresponding reaction with alkenes for the following reasons. (1)... 

On the other hand, its cycloadditions with 1,2-disubstituted alkenes under similar conditions produce stereospecifically a mixture of regioisomeric products [35] (equation 34) In contrast, its reaction with theunsymmetrical alkyne 1 -phenyl-propyne leads to a single product [35] (equation 35)... 

Cycloaddition reactions also have important applications for acyclic chalcogen-nitrogen species. Extensive studies have been carried out on the cycloaddition chemistry of [NSa]" which, unlike [NOa]", undergoes quantitative, cycloaddition reactions with unsaturated molecules such as alkenes, alkynes and nitriles (Section 5.3.2). ° The frontier orbital interactions involved in the cycloaddition of [NSa]" and alkynes are illustrated in Fig. 4.13. The HOMO ( Tn) and LUMO ( r ) of the sulfur-nitrogen species are of the correct symmetry to interact with the LUMO (tt ) and HOMO (tt) of a typical alkyne, respectively. Although both... 

The 3-oxo-2-pyrazolidinium ylides 315, easily available by reaction of the corresponding pyrazolidin-3-one with aromatic aldehydes, function as 1,3-dipoles in cycloaddition reactions with suitable alkenes and alkynes to provide the corresponding products. When unsymmetrical alkynes are used, mixtures of both possible products 316 and 317 are usually obtained (Equation 45). The regioselectivity of cycloadditions of the reaction with methyl propiolate is influenced by the substituents on the aryl residue using several 2,6-di- and 2,4,6-trisubstituted phenyl derivatives only compound 316 is formed <2001HCA146>. Analogous reactions of 3-thioxo-l,2-pyrazolidinium ylides have also been described <1994H(38)2171>. 

The triphenyl derivative (91, R = R = R = Ph, R = H) is formed in a mechanistically interesting reaction between benzoyl formic acid anil (Ph-N=CPh-C02H), trifluoroacetic anhydride, and pyridine. Its 1,3-dipolar cycloaddition reactions with alkynes and alkenes have been reported. ... 

Isosydnones (146) react with alkynes to give pyrazoles (150). For example, 4,5-diphenylisosydnone (146, R = R = Ph) and ethyl phenyl propiolate gives 4-ethoxycarbonyl-l,3,5-triphenylpyrazole (150, R = R = R = Ph, R = CO Et) identical with the product from 4,5-diphenylsydnone (1, R = R = Ph). The rate of 1,3-cycloaddition for isosydnones (146) is relatively slow in comparison with sydnones (1).2o, 04 number of other cycloaddition reactions of isosydnones with alkenes, alkynes, and carbonyl compounds have been reported. ... 

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