Cycloaddition of benzothiete and electron-deficient nitriles

The o-quinoid 8π electron system 2 , generated by thermal ring opening of benzothiete ( 1 ), enters regio-specific [8π + 2π] cycloaddition reactions with electron-deficient nitriles 3a-d , yielding the 4H-1,3-benzothiazines 4a-d. A competitive dimerization of 1 leads to 1,5-dibenzo[b,f]dithiocin (5). Depending on the nitrile further competitive or subsequent reactions (2 + 3b → 7b, 2 + 3d → 4d → 8d) can occur. The cycloadducts 10e and 11e gained from 3e anticipate a primary cleavage of 3e to methylisothiocyanate 9e which reacts at the C?N double bond as well as at the C?S double bond.     

Mechanism of reactions of acyl isocyanates with azomethines

Conclusions A study of the isomerization of the adducts, and the isolation of the free bipolar ion from the reaction of trichloroacetyl isocyanate with p-dimethylaminobenzalaniline, disclosed that the reaction of acyl isocyanates with azomethines belongs to the type of 1,4-dipolar cycloaddition.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 953–954, April, 1977.     

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 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 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.     

Cycloaddition reactions of dihapto-coordinated furans

Complexes of the type [TpRe(CO)(L)(eta(2)-furan)], where Tp = hydridotris(pyrazolyl)borate and L = PMe(3) (1) or (t)BuNC (2), undergo dipolar cycloadditions with TCNE (tetracyanoethylene) to afford 7-oxabicycloheptene complexes 3 and 4, respectively. The corresponding 2-methylfuran complexes (5 and 7) for these L ligands give similar methyloxabicycloheptene complexes (6 and 8), with a diastereomer ratio >20:1 for 8. For L = N-methylimidazole (MeIm, 9), TCNE oxidizes the complex, but cycloadditions can be achieved with DMAD (dimethyl acetylenedicarboxylate) as the electrophile. Three complexes are observed: one in which DMAD undergoes a cycloaddition with the carbonyl ylide form of the complex (10C), and two complexes that are coordination diastereomers where DMAD has undergone a formal [2+2] cycloaddition with the uncoordinated double bond of the 4,5-eta(2)-furan ligand (10B and 10A). With the imidazole complex of 2-methylfuran (11), only the [2+2] products (12B and 12A) are observed. In the case of the 2,5-dimethylfuran complex (L = MeIm, 13), which is formed as a single coordination diastereomer, only one [2+2] product is observed (14), the structure of which was confirmed by X-ray crystallography. Oxidative decomplexation of 14 results in liberation of the free oxabicyclo[3.2.0]heptadiene 15, which can be thermally converted to the corresponding oxepin 16 in 70% yield.     

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 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 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.     

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 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 with 2,3‐benzodiazepine derivatives

We report here on some 3+2 dipolar cycloaddition reactions of propargyl, allyl and cyano substituted 2,3‐benzodiazepines with in situ generated nitrile oxides and diazomethane. The reactivity of carbon‐nitrogen double bonds of the 5H‐[2,3]benzodiazepine ring system was also noticed.     

Cycloaddition reactions of cyclic ketene-N,S-acetals with 1,2,4,5-tetrazines

Reaction of 3,6-diphenyl-, 3,6-bis(2-pyridyl)- and the unsubstituted 1,2,4,5-tetrazine with 4,5-dihydro-1-methyl-2-(methylthio)pyrrole ( 2 ) and 1-raethyl-2-(methylthio)-4.5,6,7-tetrahydroazepine ( 3 ) gives 4,7-di-R-2,3-dihydro-1-methylpyrrolo[2,3-d]pyridazine ( 4 , R = phenyl, 2-pyridyl, hydrogen) and 6,9-di-R-1-methyl-2,3,4,5-tetrahydropyridazino[4,5-6]azepine ( 5 ), R = phenyl, 2-pyridyl, hydrogen), respectively, in reasonable to good yields. The compounds 4 (R = phenyl, hydrogen) are converted into their corresponding 1-methylpyrrolo-[2,3-d]pyridazines 6 by reaction with potassium permanganate in butanone. Reaction of 3-phenyl-1,2,4,5-te-trazine with 2 and 3 leads to the exclusive formation of the 7-phenyl isomer 4d and 9-phenyl isomer 5d , respectively, indicating that the cycloaddition is regiospecific. The mechanism is discussed.