Photochemical and thermal (2+2)-cycloaddition of thioxanthenethione to some aliphatic pentatetraenes

Reaction of thioxanthene-9-thione 1 with the alkyl substituted pentatetraenes 2a-g gives mixtures of the thietanes 3a-g and 4a-g. The ratio $\text{3}\text{4}$ in the thermal reaction is strongly dependent on the substituents. In the case of 2a thermal rearrangement of the product leads to a stable thiete.     

(2+2)-cycloaddition of triazolinediones to strained bicycloalkenes

Substituted norbornenes and dibenzobarrelene react under forced conditions with $\text{N}$-methyl-1,2,4-triazolin-3,5-diones to afford urazoles via (2+2)-cycloaddition.     

Features of the (2+3)-cycloaddition of trifluoroacetonitrile oxide

The (2+3)-cycloaddition of trifluoroacetonitrile oxide is a function of the donor and steric properties of dipolarophiles and usually proceeds regiospecifically. A significant temperature effect was found for the cycloaddition of trifluoroacetonitrile oxide to dipolarophiles with low donor capacity.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 972–974, July, 1989.     

Electronic factors in (4 + 2)-cycloaddition reactions of phosphaalkenes

Reactions involving the (4 + 2)-cycloaddition of phosphaalkenes to 1,3-butadiene have been characterized in the framework of the frontier-orbital approach. MNDO and nonempirical calculations in the 4-31G basis have shown that most of these reactions take place under normal electronic conditions. The -electronic stabilization energies of the transition states of the reactions have been evaluated. The influence of substituents on the relative rate and regioselectivity of the reactions of phosphaalkenes with derivatives of 1,3-butadiene has been considered.Institute of Organic Chemistry, Academy of Sciences of the Ukrainian SSR, Kiev. Scientific-Research Institute of Technical Physics, Far-Eastern University. Vladivostok. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 4, pp. 462–466, July–August, 1991. Original article submitted October 12, 1990.     

Photochemical [2+2]-cycloaddition of cyclic α,β-enones to monosubstitüted acetylenes

The photo addition of cyclic α,β-enones to monosubstituted acetylenes gives substituted bicyclo [3,2,0]hept-6-en-2-ones and bicyclo[4,2,0]oct-7-en-2-ones. The addition of 2-cyclopentenone to different substrates of type RCCH (where R is alkyl, CH₂X, OEt, COOMe and also Ph) and addition of 2-cyclohexenones to 1-hexyne show a linear correlation between the σ-constants of substituents and the rates of cycloaddition. The reaction can be qualified as a moderately electrophilic attack of the enone triplet on the acetylenic bond (¦?¦~1.5). Temperature and solvent effects on the rates and regioselectivity were also studied. The regioselectivity of addition of these α, β,-unsaturated ketones to 1-alkynes does not correspond to what might be expected on the basis of Corey's orientation rule. The addition of 2-cyclopentenone to ethoxyacetylene 3g and to methyl propiolate3h proceeds with surprisingly low regioselectivity while phenylacetylene 3i undergoes only dimerization under photoannelation conditions.     

Synthesis of phenanthrene derivatives through the net [5+5]-cycloaddition of prenylated carbene complexes with 2-alkynylbenzaldehyde derivatives

The reaction of prenylated carbene complexes and 2-alkynylbenzoyl derivatives has been investigated. Phenanthrene derivatives are produced if iodine is added prior to product isolation. Under these conditions alkyl migration reactions occur to form the observed products. The product yields are considerably higher using bis(prenylated) species owing to an increase in the effective molarity of dienophilic entities.     

Synthesis of furanophane derivatives through [8+2]-cycloaddition of dienylisobenzofurans and alkynes

The coupling of various dienylisobenzofurans with dimethyl acetylenedicarboxylate (DMAD) has been examined. In most cases, this reaction proceeds via [8+2]-cycloaddition to afford furan-bridged decatetraene ring systems. The major competing reaction pathway is [4+2]-cycloaddition between DMAD and the isobenzofuran nucleus. Isobenzofuran intermediates were generated using either a chromium carbene-based method or an acid-catalyzed method.     

Combining bifunctional chelator with (3 + 2)-cycloaddition approaches: synthesis of dual-function technetium complexes

A new concept for the synthesis of dual-functionalized technetium (Tc) compounds is presented, on the basis of the reactivity of fac-{Tc(VII)O(3)}(+) complexes. The concept combines the "classical" bifunctional chelator (BFC) approach with the new ligand centered labeling strategy of fac-{TcO(3)}(+) complexes with alkenes ((3 + 2)-cycloaddition approach). To evidence this concept, fac-{(99)TcO(3)}(+) model complexes containing functionalized 1,4,7-triazacyclononane (tacn) derivatives N-benzyl-2-(1,4,7-triazonan-1-yl)acetamide (tacn-ba) and 2,2',2″-(1,4,7-triazonane-1,4,7-triyl)triacetic acid (nota·3H) were synthesized and characterized. Whereas [(99)TcO(3)(tacn-ba)](+) [2](+) can be synthesized following a established oxidation procedure starting from the Tc(V) complex [(99)TcO(glyc)(tacn-ba)](+) [1](+), a new synthetic pathway for the synthesis of [(99)TcO(3)(nota)](2-) [5](2-) had to be developed, starting from [(99)Tc(nota·3H)(CO)(3)](+) [4](+) and using sodium perborate tetrahydrate (NaBO(3)·4H(2)O) as oxidizing reagent. While [(99)TcO(3)(nota)](2-) [5](2-) is a very attractive candidate for the development of trisubstituted novel multifunctional radioprobes, (3 + 2)-cycloaddition reactions of [(99)TcO(3)(tacn-ba)](+) [2](+) with 4-vinylbenzenesulfonate (styrene-SO(3)(-)) demonstrated the suitability of monosubstituted tacn derivatives for the new mixed "BFC-(3 + 2)-cycloaddition" approach. Kinetic studies of this reaction lead to the conclusion that the alteration of the electronic structure of the nitrogen donors by, e.g., alkylation can be used to tune the rate of the (3 + 2)-cycloaddition.     

Solvent dependence of singlet oxygen / substrate interactions in ene-reactions, (4+2)- and (2+2)-cycloaddition reactions

Product formation of singlet oxygen reactions with simple olefins occurring as ene-reactions, (4+2)- and (2+2)-cycloaddition reactions is independent on solvent polarity. Thus, 2,3-dimethyl-2-butene (1) and 2-methy]-2-butene (3), 1,3-cyclohexadiene (6), and benzvalene (8) yield allylic hydroperoxides (2) and(4) (54%) + (5) (46%), endoperoxide (7), and dioxetane (9), respectively. The rates of the ene-reactions and (4+2)-cycloaddition reactions are only slightly dependent, those of the (2+2)-cycloaddition reaction, however,are clearly dependent on solvent polarity. “Physical” quenching of singlet oxygen by the olefins is negligible, but substantial by the sensitizer tetraphenylporphin (TPP) in chlorinated solvents.     

Photochemical reaction of carbazole and some derivatives in dichloromethane

By irradiation of carbazole and some derivatives in CH₂Cl₂ soln two different reaction pathways were observed depending on the substitution of the heterocyclic compound.     

Chiral bis(imidazolidine)pyridine-cu complex-catalyzed enantioselective [3+2]-cycloaddition of azomethine imines with propiolates

[3+2] Cycloaddition of azomethine imines with electron-deficient terminal alkynes was smoothly catalyzed by a chiral bis(imidazolidine)pyridine-CuOAc complex to give bicyclic pyrazolo[1,2-a]pyrazolone derivatives with up to 74% ee.     

Vinyl-aziridines and cyclopropanes in Pd-catalyzed (3+2)-cycloaddition reactions with cyclic N-sulfonyl imines

Efficient palladium-catalyzed (3 + 2)-cycloaddition reactions of cyclic N-sulfonyl imines and vinyl-aziridines (or cyclopropanes) have been achieved. The reactions, with either vinylic substrate, proceed with excellent yields affording highly functionalized imidazolidine and pyrrolidine derivatives. The cycloadditions take place via the reaction of zwitterionic π-allyl palladium intermediates with cyclic N-sulfonyl imines through i) the formation of two NC bonds in the presence of vinylaziridines (synthesis of imidazolidines) and ii) one CC bond and one NC bond in the presence of vinylcyclopropanes (synthesis of pyrrolidines). Following on preliminary works on the diastereoselective synthesis of imidazolidines, herein we wish to give a broader view on the subject by describing derivatization reactions and attempts towards an enantioselective version. Moreover, we describe and discuss the behavior of each vinylic substrate (aziridine or cyclopropane) on the (3 + 2)-cycloaddition reactions. Mechanistic and (intriguing) selectivity outcomes are also going to be discussed.     

(4+2)-cycloaddition of nitroalkenes with ynamines; formation of a 4H-1,2-oxazine 2-oxide derivative

The formation of a thermally unstable (4+2)-cycloadduct, a 4H-1,2-oxazine 2-oxide derivative ($\text{1}$), from the reaction of 1-nitrocyclopentene with 1-phenyl-2-(1-pyrrolidinyl)acetylene has been proven by the structure elucidation of isoxazole derivative $\text{3}$ which results from thermal rearrangement and by the structure determination of the 1,3-dipolar adducts $\text{5}$ of $\text{1}$ with electron-deficient acetylenes.     

Arylmethylene-3H-furan(pyrrol)-2-ones in reactions of [3+2]-cycloaddition with activated hydrazones

Spiropyrrolidine derivatives were synthesized for the first time by [3+2]-cycloaddition of 3-arylmethylene-3H-furan(pyrrol)-2-ones to N-benzylidenebenzylamine activated by the system AcOAg-Et₃N. The reaction route and the spectral characteristics of the first obtained compounds have been discussed.     

An auxiliary induced asymmetric synthesis of functionalized cyclobutanes by means of catalytic (2+2)-cycloaddition reaction

A new entry to optically active hydroxycyclobutanes is described. Treatment of silyl enol ether and (−)-8-phenylmenthyl acrylate in the presence of a catalytic amount of EtAlCl₂ affords enantiomerically enriched multi-substituted cyclobutane compounds in a good yield and diastereofacial selectivity.     

Reduction of tetrakis(trimethylsilyl)butatriene by lithium: Monomeric and dimeric structures of the dilithium butatriene dianion

Treatment of tetrakis(trimethylsilyl)butatriene (2) with lithium in tetrahydrofuran (THF) led to quantitative formation of the corresponding dianion species. Yellow crystals of the dilithium salts of 2 were isolated as an unexpected dimeric structure (4) as well as a monomeric structure (3). Both of the crystal structures, which havebeen confirmed by X-ray diffraction, reveal a doubly bridged lithium bisallylic structure. The unique dynamic behaviour of the lithium ions of the dimer 4 in toluene-d₈ is demonstrated.     

Methylenecyclopropane in the [2+2+1]-cycloaddition reaction with dicobalt-hexacarbonyl complexes of acetylenes

The ability of methylenecyclopropane to undergo [2+2+1]-cycloaddition reactions with dicobalt-hexacarbonyl complexes of alkynes with formation of spiro[2,4]-heptenone derivatives has been revealed for the first time. The conditions for carrying out this reaction on the surface of adsorbents and zeolites have been established, so that it can be considered as a general preparative method for the preparation of various derivatives of spiro[2,4]heptenones (yields up to 80%). With monosubstituted acetylenes, the [2+2+1]-cycloaddition proceeds regioselectively, giving preferentially cyclopentenones containing a spiro fragment in the -position to the carbonyl. In the case of disubstituted acetylenes, -isomers are formed exclusively.For previous communication; see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2061–2068, September, 1989.