Nitrene insertion reactions. Part III. The steric effect of the Isopropyl and t-butyl groups. 1,6 Type cycloaddition of tetracyanoethylene to 1H-azepines

Various alkyl and aryl carboxynitrenes generated thermally from the azidoformates react with para-di-t-butylbenzene with a high degree of selectivity to yield predominantly, or exclusively, 3,6-di-t-butylazepine-N-carboxylates. 3,6-Dialkylazepines react readily with tetracyanoethylene to afford the first known TCNR-1H-azepine cycloadducts of the 1,6 type.     

Nitrene addition to a mesoionic 4-thiazolone. A probable (1+3) cycloaddition

The reaction of mesoionic 4-thiazolones with ethyl azidoformate (at 130°) gave 5-(ethoxy-carbonylthio)-1-imidazolin-4-ones, probably via a bicyclic nitrene-mesoion adduct.     

Formation of a bridging-imido d6 rhodium compound by nitrene capture. insertion and cycloaddition reactions

The first d (6) rhodium imido complex, [{(C 5Me 5)Rh(mu-NSO 2C 6H 4Me- p)} 2] ( 2), has been obtained from the reaction of [(C 5Me 5)Rh(C 2H 4) 2] with chloramine-T. Carbon monoxide inserts into the N-Rh bonds in 2 to give the dinuclear ureylene complex [(C 5Me 5)Rh(mu-{(Ts) N-CO-N(Ts)}Rh(CO)(C 5Me 5)], while the azide C 6F 5N 3 adds to 2 to give the mononuclear tetrazene complex [(C 5Me 5)Rh{( p-MeC 6H 4SO 2)N 4(C 6F 5)}].     

Fluorine-containing imines. 1. New cycloaddition reactions of acylimines of fluoroketones

Conclusions Acylimines of fluoroketones react with nitriles and aromatic aldehydes to form 1,4-cycloadducts, and with difluorocarbene give 1,2- and 1,4-cycloadducts, with the latter predominating.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1826–1830, August, 1979.     

Template effects on the asymmetric cycloaddition reaction between 3,4-dimethyl-1-phenylarsole and diphenylvinylphosphine and their arsenic elimination reaction

The organopalladium complex containing ortho-metalated (S)-[1-(dimethylamino)ethyl]naphthalene as the chiral template was employed to promote the asymmetric cycloaddition reaction between 3,4-dimethyl-1-phenylarsole and diphenylvinylphosphine. It has been proven that the chiral template incorporating napthylamine is more efficient than the benzylamine based analogue as evidenced by the drastic improvement in stereoselectivity and reaction rate. However, when no chiral template was employed, trans-[PdI₂(3,4-dimethyl-1-phenylarsole)₂] reacted with trans-[PdI₂(diphenylvinylphosphine)₂] producing a structurally novel diiodo complex, as a result of an interesting selective cleavage of one As-C bond in the norbornene skeleton and subsequent rearrangements within the skeletal framework. The molecular structure of the diiodo product has been confirmed by X-ray crystallography. Structural analysis showed that in addition to the normal As-P five-membered ring, there is one new five-membered ring containing As-O bond being formed during the course of the reaction along with another seven-membered ring incorporating a hydroxy group.     

1-Azadienes in cycloaddition and multicomponent reactions towards N-heterocycles

1-Azadienes are versatile building blocks for the efficient construction of various N-heterocycles. Depending on the substitution pattern and reaction partner, they may participate in a range of different reactions. An overview of recent methods for the generation of 1-azadienes is presented, as well as their application in cycloaddition, electrocyclization, and multicomponent reactions. Considering the broad range of reactivities and resulting heterocyclic scaffold structures, 1-azadienes are very useful reactive intermediates for the development of modular reaction sequences in diversity-oriented synthesis.     

Photochemical cycloaddition reactions of cyanoacetylene and dicyanoacetylene.

Photolysis of cyanoacetylene with 185- or 206-nm light yields 1,3,5-tricyanobenzene while 254-nm radiation yields a mixture of tetracyanocyclooctatetraenes, 1,2,4- and 1,3,5-tricyanobenzene. A polymer of cyanoacetylene is the major photoproduct. 1,3,5-Tricarbomethoxybenzene was the only photoproduct identified from the irradiation of methyl propiolate at 254 nm. Mono-, di-, and tricyanobenzenes are formed by irradiation of mixtures of acetylene and cyanoacetylene at 185, 206, and 254 nm along with trace amounts of cyclooctatetraenes. No photoadducts were detected on photolysis of mixtures of cyanoacetylene and CO or HCN. The tetracyanocyclooctatetraene structures were established by UV, MS, and NMR analyses. The 1H NMR of the product mixture exhibited a singlet at delta 7.028 consistent with either 1 or 2 and two singlets at delta 6.85 and 6.91 assigned to 3. Photolysis of mixtures of dicyanoacetylene and acetylene with either 185- or 206-nm light yielded 1,2-dicyanobenzene and (E,Z)-1-buten-3-yne-1,4-dicarbonitrile. These products were also obtained using 254-nm light along with a mixture of tetracyanocyclooctatetraenes. The same three singlets were observed in this product mixture as were observed in the tetracyanocyclooctatetraenes obtained from cyanoacetylene. From this observation it was concluded that the delta 7.02 signal is due to 2 and not 1. The photolysis of cyanoacetylene and dicyanoacetylene in the presence of ethylene with 185-nm light yields 1-cyanocylobutene and 1,2-dicyanocyclobutene, respectively. 2-Cyanobutadiene and 2,3-dicyanobutadiene are the photoproducts with 254-nm light. Reaction pathways are proposed to explain these findings.     

New cycloaddition reactions of 1-phenyl-4-vinylpyrazole

1-Phenyl-4-vinylpyrazole reacts with methyl propiolate and N-phenylmaleimide giving via the Diels-Alder 1:1 adducts, products (4) and (8), and also the 1:2 adducts (5), (6) and (9) resulting from an “ene” reaction of the initially forced cycloadducts. The obtention of the adducts (5) and (6) in equimolecular amounts is a good example of the non-regioselective character of the “ene” reaction. The reaction with tetracyanoethylene takes place through the olefinic substituent giving the π² + π² adduct (10).     

Synthesis of new beta-substituted meso-tetraphenylporphyrins via 1,3-dipolar cycloaddition reactions. 1

The azomethine ylide generated from the reaction of (beta-formyl-meso-tetraphenylporphyrinato)nickel(II) with N-methylglycine reacts with a range of dipolarophiles, yielding new beta-substituted-meso-tetraphenylporphyrins. The regio- and stereochemistry of the new compounds was established using one- and two-dimensional NMR techniques.     

Water-catalyzed dehalogenation reactions of isobromoform and its reaction products

A combined experimental and theoretical study of the photochemistry of CHBr(3) in pure water and in acetonitrile/water mixed solvents is reported that elucidates the reactions and mechanisms responsible for the photochemical conversion of the halogen atoms in CHBr(3) into three bromide ions in water solution. Ultraviolet excitation at 240 nm of CHBr(3) (9 x 10(-)(5) M) in water resulted in almost complete conversion into 3HBr leaving groups and CO (major product) and HCOOH (minor product) molecules. Picosecond time-resolved resonance Raman (ps-TR(3)) experiments and ab initio calculations indicate that the water-catalyzed O-H insertion/HBr elimination reaction of isobromoform and subsequent reactions of its products are responsible for the production of the final products observed following ultraviolet excitation of CHBr(3) in water. These results have important implications for the phase-dependent behavior of polyhalomethane photochemistry and chemistry in water-solvated environments as compared to gas-phase reactions. The dissociation reaction of HBr into H(+) and Br(-) ions is the driving force for several O-H insertion and HBr elimination reactions and allows O-H and C-H bonds to be cleaved more easily than in the absence of water molecules. This water-catalysis by solvation of a leaving group and its dissociation into ions (e.g., H(+) and Br(-) in the examples investigated here) may occur for a wide range of chemical reactions taking place in water-solvated environments.     

Synthesis of substituted [3]dendralenes and their unique cycloaddition reactions

Dimethylsulfonium methylide mediated olefination of 2-phenylethenylidene phosphonoacetate followed by the Horner-Wadsworth-Emmons reaction with aromatic aldehydes provided access to reactive 1,5-diaryl-2-ethoxycarbonyl [3]dendralenes which in situ underwent Diels-Alder cyclodimerisation leading to highly functionalised cyclohexenes with very high regio- and stereoselectivity.     

Imidazolium ylides from a conjugate addition-proton transfer route and their cycloaddition reactions

4,5-Dihydroimidazolium ylides formed by conjugate addition-proton transfer from dihydroimidazoles and doubly-activated electron-deficient alkenes afford 2:1 cycloadducts in a one-pot process wherein the alkene also acts as a dipolarophile.     

The preparation and cycloaddition reaction of 1-sulfonyl-1-trifluoromethyl allenes

A series of 1-sulfonyl-1-trifluoromethyl allenes were prepared for the first time from commercial available 2-bromo-3,3,3-trifluoropropene. Cycloaddition reaction of these trifluoromethylated allenes with nitrones occured readily under mild conditions, giving the corresponding trifluoromethylated isoxazolidines in high yields.     

Synthesis of oximes,conversion to nitrile oxides and their subsequent 1,3-dipolar cycloaddition reactions under microwave irradiation and solvent-free reaction conditions

Aldoximes and ketoximes were readily synthesized from aldehydes and hydroxylamine hydrochloride on Al₂O₃ without solvent under microwave irradiation. At higher irradiation power, aldoximes dehydrated to nitriles and ketoximes rearranged to amides. Aldoximes reacted in a one-pot reaction with N-chlorosuccinimide and alkenes or alkynes over alumina under microwave irradiation to give isoxazolines or isoxazoles. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:351–354, 1998     

1,3-Dipolar cycloaddition reactions of 3-acylimino-1-methylbenzimidazolium betaines

3-Acylimino-1-methylbenzimidazolium betaines undergo 1,3-dipolar cycloaddition reactions with activated alkenes (methyl acrylate, acrylonitrile, and fumaronitrile) and methyl propiolate to produce 2-substituted 1-methylbenzimidazoles. The transformation involves the initial formation of a 1,3-dipolar cycloadduct followed by the N? N bond cleavage. The primary adducts can be isolated from the reaction with methyl acrylate and acrylonitrile.     

Cycloaddition reactions of cephalosporin compounds. XI. 1,3-dipolar cycloaddition reaction of an exo-2-methylenecephem with diphenyldiazomethane

In the 1,3-dipolar cycloaddition reaction of the exo-2-methylenecephem 6 with diphenyldiazomethane the initially formed pyrazolines decompose and spirocyclopropylcephalosporin formation takes place. The structure elucidation with ¹H, ¹³C, ASIS and NOE nmr methods is also described.