Cycloaddition reactions of polysubstituted furans with oxyallyl carbocations

New and improved routes to polysubstituted furans are described, together with a survey of their reactivity in cycloaddition reactions with oxyallyl carbocations, producing polysubstituted 8-oxabicyclo[3.2.1]oct-6-en-3-ones.     

[3 + 4] Cycloaddition reactions of vinyl carbenoids with furans

The rhodium(II) acetate catalysed decomposition of diethyl 4-diazopent-2-enedioate in the presence of furans results in the formation of products derived from a [3 + 4] cycloaddition.     

Cycloaddition reactions of thiiranimines

Thiiranimines have been found to cycloadd by the three pathways shown in Scheme 1. The reactions are examplified with enamines (path a), ynamines (path b) and aldehydes (path c).     

Cycloaddition reactions of heterophospholes

The cycloaddition reactions namely, [2 + 4], [4 + 2], [2 + 3] and [1 + 4] given by the heterophospholes, which are five-membered 6π aromatic heterocycles containing at least one σ², λ³ phosphorus, are reviewed in the present article. Different aspects of these reactions such as stereoselectivity, regioselectivity, relative reactivities and theoretical correlations thereof are included. The literature has been surveyed up to December 2003. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:271–287, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20002     

Cycloaddition reactions of 3-vinylthiophen

Cycloaddition reactions between 3-vinylthiophen and the dienophiles maleic anhydride, methyl acrylate, dimethyl acetylene - dicarboxylate, and methyl propiolate give products including methyl benzo[b]thiophen-7-carboxylate (11) and its dihydroderivative (10), the 6,7-dicarboxylic acid (3), its dimethyl ester (7) and dihydroester (6); the naphtho[a,b]dithiophen (14), and the novel ethano bridged benzo[b]thiophen (15).     

Cycloaddition reactions of 2-vinylthiophen

Cycloaddition reactions between 2-vinylthiophen and the dienophiles maleic anhydride, dimethyl acetylenedicarboxylate,' methyl propiolate, and methyl acrylate, are reported. Products include simple benzo[b]thiophen carboxylates (6, 13, 17) and reduced derivatives (3, 4, 18). The acetylenic dienophiles also gave a dihydrobenzthienyl-acrylate (16) or -fumarate (11), and the dithienylcyclohexene esters (7) and (14).     

Cycloaddition reactions of 3-fluorobutenone

3-Fluorobutenone (8) reacted as a dienophile with several dienes 9, 11, 13, 15, 17 to give cycloaddition products in moderate yields. The regio- and stereoselectivity of the reactions are given. Compound 8 is slightly less reactive than methyl vinyl ketone.     

Cycloaddition reactions of cross-conjugated enaminones

A detailed study on the cycloaddition reactions of cross-conjugated enaminones 1 and 9 with dimethyl acetylenedicarboxylate (DMAD) and ketenes is described. The reactions provide a variety of pyran (4, 11), pyran-2-one 14 and pyrrol-3-ylidene 8 derivatives having great pharmacological and medicinal significance. Moreover, the preferred formation of product 8 over 7 has been explained on the basis of molecular dynamics (MD) simulations performed on the intermediate 5 in the gas phase. The synthetic potential of enaminones 9 has further been explored by treating them with Lawesson's reagent (LR) and trapping the in situ generated enaminothiones 16 with some acrylates 17 leading to the formation of thiopyran derivatives 19. To the best of our knowledge, this is the first report in which cross-conjugated enaminothiones 16 have been utilized in cycloaddition reactions.     

The diels-alder reactions of furans 1: the reactions of furans with α-chloroacryonitrile

The intermolecular Diels-Alder reactions of several furans with α-chloroacrylonitrile occurs at atmospheric pressure. The role of temperature in affecting starting material: product ratio is examined from a preparative viewpoint.     

Synthesis and reactions ofβ-substituted furans

3-Bromofuran has been obtained in good yield by the reaction of 4, 5-dibromo-3, 6-endoxohexahydrophthalic anhydride with quinoline at 210–220° C. It has been shown that the reaction of 3-bromofuran with acetic anhydride in the presence of perchloric acid forms 2-acetyl-3-bromofuran.     

Cycloaddition reactions of β-trifluoroacetylvinyl ethers

β-Trifluoroacetyl vinyl ethers ROCHCHCOCF₃ react smoothly as dienophiles with α,β-unsaturated carbonyl compounds to give the unexpected 2-alkoxyl-5-trifluoroacetyl-3,4-dihydro-2H pyrans. These products are formed by elimination and addition of the alcohol to the products of the normal hetero Diels-Alder reaction (2-alkoxyl-3-trifluoroacetyl-2,3-dihydro-2H pyrans). In contrast, 1,3-dipolar cycloaddition of ROCHCHCOCF₃ with ArCHN(O)Me proceeds via a Z-endo transition state to give regio- and stereospecific 4-trifluoroacetyl substituted isoxazolidines and their derivatives.     

Cycloaddition reactions of benzyne with olefins

Some novel cycloaddition reactions based on benzyne and olefins have been developed.These reactions were performed in the absence of a transition metal catalyst,and they displayed good yields.These cycloaddition reactions of benzyne with olefins provide effective routes for synthesizing benzocyclobutenes,biaryl compounds and 9,10-dihydrophenanthrene derivatives.     

Cycloaddition reactions of methyl 2-N-trifluoroacetyliminotrifluoropropionate

Conclusions The methyl ester of 2-(N-trifluoroacetylimino)trifluoropropionic acid reacts with diazo-alkanes at the isolated C=N bond similarly to azomethines, forming [1+2]- and/or [3+2]-cycloadducts, and with unsaturated donating type compounds as a 1,3-dipolar conjugated system to give products of [2+4]-cycloaddition regio- and stereo-selectively.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 132–136, January, 1988.     

Cycloaddition reactions of benzothiete with azomethines

A new synthetic route to 3,4-dihydro-2H-1,3-benzothiazines 5 has been developed by the regiospecific cycloaddition of Schiff bases 4 and benzothiete 1 , which is primarily opened by heating to the corresponding o-quinoidal form 2 .     

Cycloaddition reactions of 1-tert-butyl-4-vinylpyrazole

Summary 1-tert-Butyl-4-vinylpyrazole1 a reacts with dimethyl acetylenedicarboxylate (DMAD), methyl propiolate (MP) and N-phenylmaleimide (NPMI) affording the indazole derivatives2,3, and5 as a result of a Diels-Alder ([4 + 2]) cycloaddition. With diethylazodicarboxylate (DEAZD), tetracyanoethylene (TCNE) and 4-phenyl-1,2,4-triazole-3,5-dione (PTAD) the reaction takes place exclusively through the olefinic substituent and the adducts6,7, and9 were isolated. The alkenylpyrazoles1 b–d reacted withDMAD and N-phenylmaleimide to give polymers.

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Cycloadditionen von 1-tert-Butyl-4-vinylpyrazol

Zusammenfassung 1-tert-Butyl-4-vinylpyrazol1 a reagiert mit Acetylendicarbonsäure-dimethylester (DMAD), Propiolsäuremethylester (MP) und N-Phenylmaleimid (NPMI) zu den entsprechenden Indazolderivaten2,3 bzw.5, als Ergebnis einer Diels-Alder-([4+2])-Cycloaddition. Bei der Reaktion mit Azodicarbonsäure-diethylester (DEAZD), Tetracyanethylen (TCNE) und 4-Phenyl-1,2,4-triazol-3,5-dion (PTAD) wird exklusiv die Olefingruppe von1 a angegriffen, wobei die Addukte6,7 bzw.8 isoliert werden. Die Alkenylpyrazole1 b–d reagieren mitDMAD und N-Phenylmaleimid unter Bildung von Polymeren.

     

Cycloaddition reactions of 1,3-diacetylimidazolin-2-one

1,3-Diacetylimidazolin-2-one, for which a new preparation is described, has been found to undergo thermal cycloaddition reactions with a limited number of dienes; in contrast it undergoes photochemical cycloadditions quite readily.