Synthesis of [1,3]dithiole and spiro[1,3]dithiole thiopyran derivatives of the [1,2]dithiolo[1,4]thiazine ring system

We report the synthesis of some new polysulfur-nitrogen heterocycles by cycloaddition reactions to readily available tricyclic condensed 1,2-dithiole-3-thiones. Thus, treatment of bis[1,2]dithiolopyrrole ketothione 1 with diacyl acetylenes gave the bis-aducts 2a-d. On the other hand, cycloaddition of bis[1,2]dithiolo[1,4]thiazine ketothione 3 with 1 equiv of acyl or diacyl acetylenes gave [1,3]dithiolylidenyl[1,2]dithiolo[1,4]thiazines 4a-f in fair to high yields. Catalysis by scandium triflate was used in the reactions that implied the less reactive dipolarophiles. Treatment of 3 with 2 equiv of DBA gave the bis-aduct 5a, and reaction of 4c with DMAD gave the mixed bis-adduct 5b. Cyclic voltammetry of selected examples showed irreversible processes that were influenced by the electrochemical activity of peripheral groups bonded to the heterocyclic system.     

Simple preparation of diamondoid 1,3-dienes via oxetane ring opening

The transformations of apical mono- and bisacetyl diamondoids to the respective oxetanes and subsequent acid-catalyzed ring opening/dehydration lead to diamondoidyl mono- and bis-1,3-dienes in high preparative yields.     

Preparation of partially substituted 1-halo- and 1,4-dihalo-1,3-dienes via reagent-controlled desilylation of halogenated 1,3-dienes

Depending on the desilylation reagents used, 1-halo-1,4-bis(trimethylsilyl)-1,3-butadienes afforded either 1-halo-1-trimethylsilyl-1,3-butadienes or 1-halo-4-trimethylsilyl-1,3-butadienes in excellent yields with excellent selectivity, respectively, when treated with CF3COOH or with NaOMe. These monosilylated 1,3-butadiene products could be further desilylated to generate their corresponding halobutadienes via the above reagent-controlled desilylation reaction. When 1,4-dihalo-1,4-bis(trimethylsilyl)-1,3-dienes were treated with MeONa/MeOH at room temperature, desilylation of both of the two trimethylsilyl groups took place to afford their corresponding 1,4-dihalo-1,3-dienes in excellent yields. The commonly used desilylation reagent CF3COOH did not work for these dihalobutadienes.     

A new palladium-catalysed synthesis of 1,1-dialkylbuta-1,3-dienes via organoboron intermediates

Iodobenzene and tetrakis(triphenylphosphine)palladium(0) [(C6H5)3P]4Pd catalyse a new synthesis of 1,1-dialkylbuta-1,3-dienes, starting from 1,1-diethoxybut-2-ene and trialkylboranes, in the presence of Schlosser's superbase LIC-KOR.     

Synthesis of benzo[b]furans via CuI-catalyzed ring closure

A wide variety of benzo[b]furans were synthesized efficiently via a CuI-catalyzed ring closure of 2-haloaromatic ketones. The methodology was tolerant to various functional groups, affording benzofurans in 72-99% yields.     

Zur elektronischen struktur von 6,6′-dimethylfulven und spiro[2.4]Hepta-4,6-dien

The electronic structure of cations 1 and 2 is compared with those of the neutral compounds 3–5. Distinction about the magnitude of aromatic character in the five-membered ring of 3 and 4 vs 5 is made using ¹³C-nuclear magnetic resonance. The results of the experimental investigations are compared with those derived from optimized semi-empirical MINDO/2 calculations using Ruedenberg's energy partitioning technique.     

Assembling of 3,6-diazabicyclo[3.1.0]hexane framework in oxidative triflamidation of substituted buta-1,3-dienes

Reaction of trifluoromethanesulfonamide (triflamide) CF₃SO₂NH₂ with 2,3-dimethylbuta-1,3-diene (2) and 2,5-dimethylhexa-2,4-diene (3) in the oxidative system (t-BuOCl+NaI) results in the formation of 2,4-dimethyl- or 2,2,4,4-tetramethyl-3,6-bis(triflyl)diazabicyclo[3.1.0]hexane through two successive heterocyclizations. Reaction of diene (3) with arenesulfonamides ArSO₂NH₂ (Ar=Ph, Tol), stops at the formation of the product of oxidative 1,4-addition, N,N′-(2,3-dimethylbut-2-ene-1,4-diyl)diarenesulfonamides, providing evidence of the essential difference between the reactivity of triflamide and arenesulfonamides.     

The formation of tetracyclo[7.2.1.02,5.02,8]dodeca-6,10-dienes under conditions of thermal isomerization of spiro[2.4]hepta-4,6-diene into bicyclo[3.2.0]hepta-1,3-diene

The formation of the novel hydrocarbons, tetracyclo[7.2.1.0^2,5.0^2,8]dodecadienes, as a result of thermal isomerization of spiro[2.4]hepta-4,6-diene into bicyclo[3.2.0]hepta-1,3-diene and its capture by 1,3-dienes is demonstrated. The conditions of thermal isomerization and dimerization of the spiroheptadiene are studied. Cyclopropanation of the polycyclic dienes formed by diazomethane in the presence of Pd-catalysts was accomplished, and occured solely through the norbornene double bond.For preliminary communication see ref.¹ Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 132–137, January, 1993.     

Formation of 2,6-dioxabicyclo[3.3.0]-octa-3,7-dienes or multiply substituted o-benzoquinones from reactions of 1,4-dilithio-1,3-dienes with dimethyl oxalate

Reactions of 1,4-dilithio-1,3-dienes with dimethyl oxalates afforded multiply substituted o-benzoquinones or stereodefined 2,6-dioxabicyclo[3.3.0]-octa-3,7-dienes in good yields.     

Chemoselective ring closure of thiacalix[4]arene-1,3-bis(N-ω-hydroxyalkylamides) via the Mitsunobu reaction

Chemoselective intramolecular ring closure on the phenolic OH groups of p-tert-butylthiacalix[4]arene-1,3-bis(N-ω-hydroxyalkylamides) attained under Mitsunobu conditions affords inherently chiral macrocycles capped by carboxamide bridges. Oxazoline or oxazine cyclization products derived from self-condensation of the hydroxyalkylamide moieties were not isolated. In one case the detection of enantiomers was achieved by chiral HPLC.     

Photochemical eliminations involving zwitterionic intermediates generated via electrocyclic ring closure of benzothiophene carboxanilides

Leaving groups such as carboxylate, thiolate, and phenolate are expelled via zwitterionic intermediates produced upon photochemical electrocyclic ring closure of benzothiophene carboxanilides in the triplet excited state. Chemical yields generally exceed 90%, while quantum yields vary with basicity of the released leaving group.     

Convenient synthesis of spiro[indoline-3,4'-pyrano[2,3-c]pyrazole] and spiro[acenaphthyl-3,4'-pyrano[2,3-c]pyrazoles] via fourcomponent reaction

The base promoted four-component reaction of hydrated hydrazine, dimethyl acetylenedicarboxylate, isatines and malononitrile (ethyl cycanoacetate) in ethanol afforded polysubstituted spiro[indoline-3,4‘-pyrano[2,3-c]pyrazoles] and spiro[acenaphthyl-3,4-pyrano[2,3-c]pyrazoles]     

Unusual formation of hydroperoxides in the reactions of substituted spiro[pyrazolinecyclopropanes]

3-Cyano- and 3-(alkoxycarbonyl)spiro[2-pyrazoline-5,1’-cyclopropane] and 5-phenylspiro[1-pyrazoline-3,1’-cyclopropane] undergo unusual transformations into 3(5)-substituted 5(3)-(2-hydroperoxyethyl)pyrazoles in the presence of atmospheric oxygen. The conditions for the formation of hydroperoxides (e.g., in oxygen-saturated solutions of spiro[2-pyrazoline-5,1’-cyclopropanes] in CHCl₃) and their conversion into (2-hydroxyethyl)pyrazoles or the corresponding nitrates under the action of nitrosating reagents were considered.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2160–2164, October, 2004.     

Spiro-compounds,synthesis and catalytic dehydrogenation of substituted spiro[5,5] undecanes

Catalytic dehydrogenation of 1-propyl-8,9-benzospiro[5,5]undecane-7-ol (5: R = H), and 1-propyl-3′-methyl-8,9-benzospiro[5,5]undecane-7-ol (5: R = Me) has been carried out to study the effect of a bulky alkyl group on the ring in the ring transformation of the spiro[5,5]undecane system. The catalytic dehydrogenation of the spiro-compound 5(R = H) gave phenanthrene and 1-ethylpyrene (minor product) and spiro compound 5(R = Me) gave only 3-methylphenanthrene. For the synthesis of 5 (R = H or Me), the anhydride (1) of 1-carboxy-2-propylcyclohexane-1-acetic acid was condensed with benzene and toluene to give 2 (R = H or Me) which was reduced catalytically to 3(R = H or Me). Intramolecular acylation of 3(R = H or Me) gave the spiroketone (4: R = H or Me) which was reduced to 5(R = H or Me).     

Nickel-catalyzed [4+3] cycloaddition of ethyl cyclopropylideneacetate and 1,3-dienes

The [4+3] cycloaddition of ethyl cyclopropylideneacetate (1) with 1,3-dienes proceeded in the presence of Ni(cod)₂-TOPP (tri-o-biphenylyl phosphite). The reaction provided a new method for the synthesis of cycloheptene derivatives. The mechanism of the reaction was proposed.