Regioselectivite de la cycloaddition dipolaire-1,3 : Reactions de dibenzo-2,3:6,7 heptafulvenes avec quelques dipoles

The addition of several 1,3-dipoles, viz. diazoalkanes, parachloro-benzonitrile oxide and azomethine ylides, to 2,3:6,7-dibenzo-heptafulvenes, occurs exclusively at the endocyclic double bond, leading respectively to pyrazolines, isoxazolines and pyrrolidines. This regiospecificity is due to steric factors which are conveniently discussed using Sustmann's variation perturbation theory.     

Multireference character of 1,3-dipolar cycloaddition of ozone with ethylene and acrylonitrile

In the present study, the concerted and stepwise reaction mechanisms for 1,3-dipole cycloaddition of ozone with ethylene (1) and acrylonitrile (2) are investigated. The stationary points are optimized by using four hybrid R(U)DFT methods. A geometry optimization method based on an approximate spin projection (AP-opt method) is applied to eliminate a spin contamination from the broken-symmetry (BS) solution. The AP-opt method reveals that a diradical intermediate for the stepwise pathway is spurious due to the spin contamination. The revised reaction profile with no diradical intermediate supports the stereospecificity. On the basis of the experimental data, the RCCSD(T) method outperforms AP-UCCSD(T), AP-UBD(T), and MkMRCCSD(4e,4o) for the systems, indicating that the RCCSD(T) method can describe the diradical character of ozone within a framework of single reference wave function. The subsequent single point energy calculations show that the highly synchronous transition state is much more favorable than the asynchronous one for 1. In the case of 2, there is not much difference between two transition states because of its asymmetric structure and charge separations in the transition states.     

Une synthese originale et inattendue d'isocoumarines fonctionnelles

Reaction of Ph₃P=CH-COOEt with ortho benzoyl benzoic acid derivatives offers an easy and surprising entry to functional isocoumarins via the thermal decomposition of the keto-ylide intermediates or by subsequent oxidization of the expected indenones.     

Equilibre conformationnel du fluoro-1 chloro-2 cyclohexane cis

The conformational equilibrium and kinetics of ring inversion are studied using essentially the fluorine lineshape. A new method for the calculation of the thermodynamic activation parameters is presented.     

1,3-Dipolar cycloaddition of 2-benzylideneindan-1,3-dione α-oxide to olefins

A carbonyl ylid, which reacts with maleic anhydride, N-phenylmaleinimide, and -nitrostyrene to form adducts resulting from 1,3-dipolar cycloaddition, is formed reversibly when 2-benzylideneindan-1,3-dione -oxide is heated (80C). The reaction proceeds regio- and stereospecifically.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1463–1466, November, 1987.     

Cycloaddition dipolaire-1,3 des arylnitriloxydes sur les dihydro-1,2 quinoleines n-substituees

The 1,3-dipolar cycloaddition reaction of arylnitrile oxideson 1,2- dihydroquinolines gives two adducts if the nitrogen atom of the dipolarphile carries benzoyl group. On the other hand the reaction provides only one adduct in the N-substituentis benzyl group. The structure of the cycloadducts has been established by spectroscopic and chemical method.     

Sur une transformation inattendue du β-methyl β-nitrostyrene en aldehyde salicylique

An unexpected route to o-hydroxybenzaldehyde is described. Thus, β-methyl β-nitrostyrene mixed with acetyl chloride and aluminium chloride at 0° yields upto 45% salicylaldehyde besides 2-acetoximino 1-chloro 1-phenyl propane and dichloromethyl benzene as minor products.     

1,3-Dipolar cycloaddition reactions of 1-methyl- and 1,3-dimethylindol-2-yl nitrile oxides

Reactions of the in situ prepared 1-methylindol-2-yl nitrile oxide ( 2a ) with dipolarophiles lead to isoxazolines 5 and isoxazoles 8 and to their chloro-derivatives 6 and 9 in good yields. Analogous reactions of the 1,3-dimethylindol-2-yl nitrile oxide ( 2b ) give the isoxazolines 10 and the isoxazoles 12 as main products as well as their oxidation products 11 and 13 in low yields. The mechanism of the reactions and the spectral elucidation of the cycloadducts are discussed.     

Reactions de cycloaddition dipolaire-1,3 des thiazolones mesoioniques avec des composes ethyleniques-1: Etude des problemes de stereochimie poses par l'approache dipole-dipolarophile

The stereochemistry of cycladducts obtained through the reaction of mesoionic thiazolones with ethylenic dipolarophiles is established. The dipole-dipolarophile approach is discussed in terms of interactions between the frontier orbitals. When the dipolarophile is acrylonitrile we note the importance of the destabilising interaction the HOMO orbitals. When the dipolarophile is vinyl ethyl ether we show that the interaction LUMO dipole-HOMO dipolarophile can be dominating.     

Regioselective 1,3-dipolar cycloaddition of nitrilimines to 2-methyl-2-vinyl oxirane

1,3-Dipolar cycloaddition of in situ generated C,N-diaryl nitrilimines to 2-methyl-2-vinyl oxirane gives rise to the regioselective formation of novel 5-(2-methyloxiranyl)-4,5-dihydropyrazole derivatives in moderate to good yields. The structures and stereochemistries of the new cycloadducts were confirmed by spectroscopic/physical methods including X-ray diffraction data.     

1,3-Dipolar cycloaddition of phthalazinium ylides to 5-arylidene-2-spirocyclohexane-1,3-dioxane-4,6-diones

Tetrahydrospiropyrrolo[2,1-a]phthalazines were synthesized by the reaction of 5-arylidene-2-spirocyclohexane-1,3-dioxane-4,6-diones with phthalazinium ylides. One of the reaction products, viz., 3-ethoxycarbonyl-2-(4-methoxyphenyl)-2′,2′-pentamethylene-1,2,3,10b-tetrahydrospiro[pyrrolo[2,1-a]phthalazine-1,5′-[1,3]dioxane]-4′,6′-dione, was studied by X-ray diffraction. The spectroscopic characteristics of the reaction products are discussed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2362–2365, October, 2005.     

Trifluoromethyl-p-tolyldiazomethane in 1,3-dipolar cycloaddition reactions

Trifluoromethyl-p-tolyldiazomethane (I) forms [3+2]-cycloadducts with activated alkenes and alkynes. The products of these regiospecific reactions are substituted pyrazolines (II)–(VI) and pyrazoles (VIII)–(X). Reaction of (I) with fumarates, trifluoropyruvates and allyl chloride is accompanied by elimination of N₂ and formation of a 1,2-bis(trifluoromethyl)stilbene. The results obtained indicate that (I) enters only the HOMO-controlled 1,3-dipolar addition reactions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1589–1593, July, 1991.     

Intermolecular 1,3-dipolar cycloaddition of benzonitrile oxide to 2H-1,3-benzothiazines and hexahydro-4H-1,3-benzothiazine

The thermal [3 + 2] intermolecular cycloaddition of benzonitrile oxide to 2H-1,3-benzothiazines 1a-g and hexahydro-4H-1,3-benzothiazine ( 5 ) gives new types of tricyclic angularly and linearly condensed 1,2,4-oxadiazolo-1,3-benzothiazine-fused nitrogen-bridgehead ring systems 2a-g, 6 .     

Synthesis of 3-thienyl substituted 2-pyrazolines by 1,3-dipolar cycloaddition

1,3,5-Trisubstituted 3-thienylpyrazolines have been prepared in high yields by the reaction of substituted,N-(P;-nitrophenyl)-3-thiophenecarbohydrazonoyl chlorides with Et₃N in CH₂Cl₂ in the presence of an excess of a monosubstituted olefin. The reaction probably occurs as 1,3-dipolar cycloaddition of the corresponding 3-thiophenecarbonitrile imines formedin situ at the double bond of the olefin.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 114–117, January, 1994.     

Microwave assisted Diels-Alder cycloaddition of 2-fluoro-3-methoxy-1,3-butadiene

The title fluorodiene (2) reacts with several dienophiles in moderate yields (20-65%, 0.5 h to 3d) when thermal activation is used. When 100 W microwave radiation is used the reaction yields (70-90%, 5-25 min) are greatly improved and the reaction times are much shorter. A microwave procedure is also used for the hydrolysis of vinyl ether cycloadducts to alpha-fluoroketones.