Three multicomponent reactions of 3,5-dimethyl-4-nitroisoxazole

The title compound is used to prepare 3-arylglutaric acids, bis-isoxazoles and bis-pyrazoles from commercially available materials. The methodologies described have afforded important synthetic intermediates in high yields and without the use of chromatography.     

Selective rearrangements of 4a,5-epoxides of 4,4-dimethyl-1,2,3,4,6,8a-hexahydronaphthalenes.

Epoxidation selectivity of a number of 4,4-dimethyl-1,2,3,4,6,8a-hexahydronaphthalenes 4 were examined. Exposure of the isolated α-epoxides 7provided excellent yields (79–92%) or rearranged fused indene-oxetanes 8. Treatment of β-epoxides 5 with BF3·OEt₂ also yields oxetanes 8 and related alcohols 9 and 10.     

Photochemistry of 6-trifluoromethyl-4,4-dimethyl-2-cyclohexenone

The photochemical behaviour of the title compound, newly synthesized in four steps from 4,4-dimethylcyclohexanone, is compared to that of 4,4-dimethyl- and 4,4,6-trimethyl-2-cyclohexenone. All three enones undergo rearrangement to bicyclo[3.1.0]hexan-2-ones and 3-isopropyl-2-cyclopentenones in benzene, t.butanol and acentonitrile, but only the CF₃-enone is also reduced to the saturated ketone in the latter two solvents.     

Facile synthesis of 3,4-dihydro-4,4-dimethyl-2H-pyran-2-one via palladium catalyzed terminal oxidation of 3,3-dimethyl-4-pentenoates

Selective terminal oxidation of 3,3-dimethyl-4-pentenoates does occur under chloride-free Wacker conditions [Pd(OAc)₂/O₂] in AcOH to give 5-acetoxy-3,3-dimethyl-4-pentenoates (7) and their analogues (2, 8) in good yields. Successive cyclization of 7 and 8 at vapor phase pyrolysis on SiO₂ affords 3,4-dihydro-4,4-dimethyl-2H-pyran-2-one (1).     

Photoaddition Reactions of 5-Fluoro-4,4-dimethyl-2-cyclopentenone

The photoaddition of 5-fluoro-4,4-dimethyl-2-cyclopentenone ( 4 ) to 2,3-dimethyl-2-butene leads specifically (in cyclohexane) and selectively (in acetonitrile) to the formation of the oxetanes 16 . The title compound is compared in its behaviour to the analogous 6-fluoro-4,4-dimethyl-2-cyclohexenone ( 1 ) and both α'-fluoro-4,4-dimethyl-2-cycloalkenones in turn are compared to the corresponding 2-cycloalkenones ( 6 and 3 ) and 4,4-dimethyl-2-cycloalkenones ( 5 and 2 ). The quantum yield for the addition of these enones to 2,3-dimethyl-2-butene and to cyclopentene are discussed.     

Mass spectra of 3,6-dihalo-4,4-dimethyl-1,4-selenasilafulvenes and 2,4-dihalo-2-dihalomethyl-3,3-dimethyl-1-selena-3-silacyclopent-4-enes

The behavior of new heterocyclic systems, viz., 3,6-dihalo-4,4-dimethyl-1,4-selena- silafulvenes 1a, b and 2,4-dihalo-2-dihalomethyl-3,3-dimethyl-1-selena-3-silacyclopent-4-enes 2a, b (Hal =Cl, Br), was studied under conditions of electron ionization and thermal decomposition. Their fragmentation is accompanied by skeletal rearrangements, and the positive charge is localized mainly on ions containing silicon. Selenasilafulvenes 1a, b form stable molecular ions. Selenasilacyclopent-4-ene 2a decomposes partially and compound 2b decomposes completely in the gas phase with the elimination of a hydrogen halide and a halogen molecules.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 639–642, March, 2005.The term “contribution” implies the ratio of the sum of peak intensities of all isotope varieties of the ion under consideration to the total ion current.     

Photochemical Reduction of 2-Bromo-4,4-dimethyl-2-cyclohexenone

The photochemical behaviour of 2-Bromo-4,4-dimethyl-2-cyclohexenone (1) was studied in 2-propanol and cyclohexane. In both solvents (n-π*)-excitation followed by intersystem crossing leads to population of a low-lying triplet (T₁) state, which can be quenched by 1,3-cyclohexadiene but does not undergo chemical transformation efficiently. (π-π*)-Excitation affords 4,4-dimethyl-2-cyclohexenone ( 2 ) as the only product. While in 2-propanol 2 is formed in 60% from the S₂-state and in 40% from the T₂-state, in cyclohexane reduction occurs exclusively from this upper triplet state. The T₂-state can also be populated via energy transfer using acetone or benzene as sensitizer. The mechanistic dissimilarities for the reduction of excited 1 in either 2-propanol or cyclohexane are discussed.     

Products of the gas-phase OH radical-initiated reactions of 4-methyl-2-pentanone and 2,6-dimethyl-4-heptanone

The gas-phase reactions of the OH radical with 4-methyl-2-pentanone and 2,6-dimethyl-4-heptanone have been investigated in the presence of NO_x. Acetone and 2-methylpropanal were identified and qualified as products of both reactions. The acetone yield from 2,6-dimethyl-4-heptanone increased after addition of NO to reacted mixtures, indicating that acetone is formed through the intermediary of an acyl radical. The acetone and 2-methylopropanal formation yields were determined to be 0.78 ± 0.06 and 0.071 ± 0.011, respectively, from 4-methyl-2-pentanone and 0.68 ± 0.11 and 0.385 ± 0.034, respectively, from 2,6-dimethyl-4-heptanone. The possible reaction mechanisms are discussed and compared with these product data, and it is concluded that the experimental data provide direct evidence for isomerization of the (CH₃)₂CHCH₂C(O)CH₂C(O) (CH₃)₂ alkoxy radical formed from 2,6-dimethyl-4-heptanone. However, the isomerization rates of the alkoxy radicals formed from the ketones depend on whether the H-atom abstracted is on a carbon atom α or β to the >C?O group, with H-atom abstraction from C? H bonds on the β carbon atoms being significantly faster than from C? H bonds on the α carbon atoms. © 1995 John Wiley & Sons, Inc.     

Ring — chain tautomerism and reactions of 4-aryl-4-hydroxy-2,3-dimethyl-3,4-dihydrophthalazinones

It has been established by IR spectroscopy that the N,N-dimethylhydrazides of 2-aroylbenzoic and benzil-o-carboxylic acids, with the exception of 2-mesitoylbenzoic acid, have the ring structure of 4-aryl- or 4-benzoyl-4-hydroxy-2,3-dimethyl-3,4-dihydrophthalazinones. The action of electrophilic agents on 4-hydroxy-2,3-dimethyl-4-phenyl-3,4-dihydrophthal-azinone under mild conditions leads to N₍₃₎-demethylation with the formation of 2-methyl-4-phenylphthalazinone.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1124–1126, August, 1973.     

Molecular and crystal structure of 2-para-toluimido-4,4-dimethyl-(4H)-1,3-thiazine

The imino structure of 2-p-toluimido-4,4-dimethyl-(4H)-1,3-thiazine (I) was demonstrated by x-ray diffraction structural analysis. Molecules of I in the crystal are linked by N-HO hydrogen bonds in infinite chains. A shortened SO intramolecular contact was found which corresponds to a secondary interaction. A mechanism was proposed for the thiazoline-thiazine rearrangement.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1638–1643, December, 1984.     

Intermolecular Pauson-Khand reactions of cyclopropene: a general synthesis of cyclopentanones

[reaction: see text] The Pauson-Khand reaction of cyclopropene with a variety of terminal alkynes has been studied. The best reaction conditions involve NMO activation in CH(2)Cl(2) at -35 degrees C. In this way, 3-substituted-bicyclo[3.1.0]hex-3-en-2-ones have been obtained in good to excellent yields. As a synthetic application, several types of substituted cyclopentenones have been prepared from these cycloadducts by protocols involving conjugate addition and reductive ring opening.     

Oxetane vs. cyclobutane formation in the photocycloaddition of enones to olefins. The photoaddition of 6-fluoro-4,4-dimethyl-2-cyclohexenone to 2,3-dimethyl-2-butene. Preliminary communication

n-π^* Excitation of 6-fluoro-4,4-dimethyl-2-cyclohexenone in the presence of 2,3-dimethyl-2-butene leads selectively to the formation of the corresponding oxetane. The factors which influence the oxetane vs. cyclobutane formation ratio in photoadditions of cyclic enones to olefins are discussed.