Light-Induced Synthesis of Tricyclic Thiolane Derivatives from 2(5H)-thiophenones via consecutive radical ring closure

Two α,β-unsaturated thiolactones, 5-(2-propynyl)-2(5H)-thiophenone (5) and 3,5-di(2-propenyl)?2(5H)-thiophenone (6) , were newly synthesized. Irradiation (λ = 300 nm) of 5 in MeOH containing cyclopentene afforded a 3:1 mixture of diasteroisomeric methyl 7-thiatricyclo[6.4.0.0^2,6]dodec-10-ene-12-carboxylates (8a/8b) , while irradiation of 6 in MeOH saturated with 2-methylpropene gives a 3:2 mixture of diastereoisomeric methyl 3,3,9-trimethyl-5-thiatricyclo[6.2.1.0^2,6]undecane-1-carboxylates ( 10a / 10b ).     

Photochemical Synthesis of 2-Alkylidene-1,3-cyclocalkanediones. Preliminary Communication

Photolysis (λ = 254 nm) of 4-(tert-butyl)-4,6,7,8-tetrahydro-7,7-dimethy-2H-1-benzopyran-2,5(3H)-dione ( 3a ) in t-BuOH affords 2-(2,2-dimethylpropylidene)-5,5-dimethyl-1,3-cyclohexanedione ( 1a ) in 80% yield via homolysis of the lactone O? CO bond and subsequent ketene elimination.     

Photoreduction of Cyclic α-Fluoroketones

Irradiation of the α-fluoroketones 1a and 6a in i-PrOH selectively affords the parent ketone 1b and 6b , respectively. It is concluded that in this solvent heterolytic C-F bond cleavage of the anion radical-formed by electron transfer to the excited fluoroketone-is a faster process than the subsequent protonation by the cation radical of the solvent. In cyclohexane 1b and 6b are only formed in minor amounts, the fluorinated RH-reduction product 4 now being the major product from 1a . In non-reducing solvents as t-BuOH or benzene 2-fluorocyclohexanone (1a) exhibits a similar behavior as cyclohexanone (1b) on excitation. The quantum yields for α-cleavage are alike for both compounds, but oxetane formation with 2-methylpropene as olefinic component occurs much more readily with 1a than with 1b .     

Photochemistry of Thiophen-2(5H)-ones

Mechanistic evidence for the light-induced ring opening of thiophen-2(5H)-ones 1 in alcohols affording α, β-unsaturated mercapto esters 2 is presented. Regio-and stereochemical aspects of the ring closure of alkenylthio (type 3 ) radicals 15 and 17 to S-heterocycles 16 and 18 , of 3-thiahex-5-enyl radicals 4 to (tetrahydrothien-3-yl)methyl radicals 6 and of (2,3-dihydrothien-3-yl)methyl radicals 30 (type 7, but-3-enyl radicals) to cyclopropane-methyl radicals 29 are discussed. Irradiation (λ 350 nm) of 1 in cyclohexane in the presence of 2,3-dimethylbut-2-ene affords [2 + 2] cycloadducts 14 albeit in very low yields.     

Photochemistry of N-(2-Cyclohexen-1-ylidene) alkylamines

Irradiation (λ = 254 nm) of N-(4,4,6,6-tetramethyl-2-cyclohexen-1-ylidene)-1,1,3,3-tetramethyl-2-cyclohexen-1-ylidene-1,1,3,3-tetramethylbutylamine (7d) , which in turn is photodecomposed by light of the same wavelength, but at a four times slower rate than it is formed. The rate of formation of photoproduct 7d is a function of the concentration of starting material 1d , suggesting the involvement of a bimolecular ( 1d ^* + 1d ) step. The structure of 7d was established by spectroscopy and by its hydrolysis to 3-cyclohexyl-4,4,6,6-tetramethyl-2-cyclohexenone ( 8 ). The previously made assumption that N-(2-cyclohexen-1-ylidene)cyclohexylamine ( 1a ) and 2,3,4,4a,5,6-hexahydroquinolines 2 photorearrange to N-cyclohexylidenecyclohexanamine 3a and 3,4,4a,5,6,8a-hexahydroquinolines 4 , respectively, via a light-induced 1,3-hydrogen shift proves incorrect.     

Photochemische Reaktionen. 121. Mitteilung. Zur Photochemie von ε,ζ-Methano-α,γ-dienonen und 7,8-Methano-1,3,5-trienen

Photochemistry of ε,ζ-Methano-α,γ-dienones and 7,8-Methano-1,3,5-trienes Irradiation of the δ-cyclopropyl-dienone (E)- 6 (λ ≥ 347 nm) gives (Z)- 6, 10 (1,5-sigmatropic H-shift), (E/Z)- 9 (electrocyclic process involving C(ε), C(ζ)-cleavage) and 11 (ring opening). The corresponding 6-cyclopropyl-triene (E)- 7 gives on singlet excitation (δ > 280 nm) 14 (1,5-sigmatropic H-shift) and, to a smaller extent, the bicyclo [3.2.0] heptenyl-dienes (E/Z)- 13 . However, on triplet excitation (λ ≥ 347 nm, benzophenone) (E)- 7 gives (E/Z)- 13 as the main products. On both ¹π,π*- and ³π,π*-excitation, (Z)- 7 and 15 are formed in small amounts.     

Photochemical Synthesis and Some Reactions of 7-Oxa-and 7-Thiatricyclo[3.2.1.03,6]octan-2-ones

Irradiation (λ = 350 nm) of newly synthesized 2-acetyl- or 2-methyl-2-(alk-2-enyl)furan-3(2H)-ones 1 and 2-acetyl- or 2-methyl-2-(prop-2-enyl)thiophen-3(2H)-ones 2 affords the corresponding 1-acetyl- or 1-methyl-substituted 7-oxa- and 7-thiatricyclo[3.2.1.0^3,6]octan-2-ones 10 and 11 , respectively, via regioselective intramolecular [2 + 2] photocycloaddition in 65–95% yield (Scheme 2). The 1-acetyl-substituted O-derivatives 10b and 10c undergo ring opening on treatment with MeONa in MeOH at–78° to afford stereoselectively methyl 3-exo-acetyl-2-oxabicyclo[3.2.0]heptane-7-endo-carboxylates 12b and 12c , respectively, while a 2:1 diastereoisomeric mixture of methyl 3-acetyl-2-thiabicyclo[3.2.0]heptane-7-endo-carboxylates 13 and 14 is obtained from the corresponding S-derivative 11b . The outcome of the Huang-Minlon reduction of the 1-methyl-substituted ketones 10a and 11a is again influenced by the heteroatom in the tricycle. While 1-methyl-7-oxatricyclo[3.2.1.0^3,6]-octane ( 15 ) is the only product from the corresponding oxatricyclooctanone 10a , a 1:2 mixture of 1-methyl-7-thiatricyclo[3.2.1.0^3,6]-octane ( 16 ) and 3-methylbicyclo[3.1.1]hept-2-ene-6-endo-thiol ( 17 ) is obtained from the analogous S-compound 11a , both products stemming from a common carbanion precursor.     

Photochemische Reaktionen. 118. Mitteilung [1] Zur vinylogen β-Spaltung von Enonen. UV.-Bestrahlung von 4-(3',7',7'-Trimethyl-2'-oxabicyclo [3.2.0]hept-3'-en-1'-yl)but-3-en-2-on

Vinylogous β-Cleavage of Enones: UV.-irradiation of 4-(3′,7′,7′-trimethyl-2′-oxabicyclo[3.2.0]hept-3′-ene-1′-yl)but-3-ene-2-on On ¹π,π*-excitation (λ = 254 nm) in acetonitrile (E/Z)- 2 is converted into the isomers 4–9 and undergoes fragmentation yielding 10 ; in methanol (E/Z)- 2 gives 7–10 and is transformed into 11 by incorporation of the solvent. On ¹π,π*-excitation (λ λ?347 nm; benzene-d₆) (E)- 2 is isomerized into (Z)- 2 , which is converted into the isomers 3 and 4 by further irradiation. ¹π,π*-Excitation (λ = 254 nm; acetonitrile) of 4 gives 6 and (E)- 9 , whereas UV.-irradiation (λ = 254 nm; acetonitrile-d₃) of 5 yields (E)- 7 and 8 . On ¹π,π*-excitation (λ = 254 nm; acetonitrile) of (E/Z)- 12 the compounds (E)- 14 and (E)- 15 are obtained.     

Solid-State Photocyclodimerization of 1-Thiocoumarin (= 2H-1-Benzothiopyran-2-one)

Irradiation (λ > 390 nm) of 2H-1-benzothiopyran-2-one ( 1 ) in the solid state affords selectively 6aα,6bα,12bα,12cα -tetrahydrocyclobuta[1,2-c:4,3-c′]bis[1]benzothiopyran -6,7-dione ( 2 ), the head-to-head (HH) cis-cisoid-cis-dimer, while irradiation of 1 in the solid state using shorter wavelengths (λ > 340 nm) affords a mixture of all four cis-fused tricyclic dimers 2 – 5 . These results represent a novel wavelength effect in solid-state photochemistry.     

Photochemistry of Isothiocoumarin (= 1H-[2]benzothiopyran-1-one)

Irradiation (λ = 350 nm) of 1H-[2]benzothiopyran-1-one ( 2 ) in the solid state affords selectively and in good yield 6aα, 6bα, 12bα, 12cα -tetrahydrocyclobuta[1, 2-c:4, 3-c′]bis([2]benzothiopyran)-5, 8-dione ( 3 ), the head-to-head (HH) cis-cisoid-cis-cyclodimer of 2 , X-Ray analysis of 2 confirms that this reaction proceeds according to the well-established topochemical principles. The same dimer 3 is obtained in low yields on irradiation of 10⁻¹ M solutions of 2 in either MeOH or MeCN, while no conversion at all is observed in benzene. On irradiation of 2 in MeCN in the presence of tetrachloroethene, the [2 + 2] photocycloadduct 4 is formed in good yield, the conversion 2 → 4 being efficiently quenched by naphthalene. In contrast, no reaction is observed -on irradiation of 2 in the presence of 2, 3-dimethylbut-2-ene, neither in polar nor in apolar solvents.     

Photochemische Reaktionen. 103. Mitteilung [1]. Zur Photochemie konjugierter Epoxy-en-carbonylverbindungen der Jonon-Reihe: UV.-Bestrahlung α,β-ungesättigter ε-Oxo-γ, δ-epoxy-carbonylverbindungen und Untersuchung des Mechanismus der Epoxy-enon/Furan-Isomerisierung

The Photochemistry of Conjugated γ,δ-Epoxy-ene-carbonyl Compounds of the Ionone Series: UV.-Irradiation of α,β-Unsaturated ε-Oxo-γ,δ-epoxy Compounds and Investigation of the Mechanism of the Isomerization of Epoxy-enones to Furanes On ¹n, π*-excitation (λ ≥ 347 nm; pentane) of the enonechromophore of 3 , three different reactions are induced: (E/Z)-isomerization to give 13 (7%), isomerization by cleavage of the C(γ)–C(δ) bond to yield the bicyclic ether 14 (36%) and isomerization by cleavage of the C(γ)? O bond to give the cyclopentanones 15 (13%) and 16 (11%; s. Scheme 2). On ¹π, π*-excitation (λ = 254 nm; acetonitrile) 13 (14%), 15 (6%), and 16 (6%) are formed, but no 14 is detected. In contrast, isomerization by cleavage of the C(δ)? O bond to give the cyclopentanone 17 (23%) is observed. The reaction 3 → 17 appears to be the consequence of an energy transfer from the excited enone chromophore to the cyclohexanone chromophore, which then undergoes β-cleavage. Irradiation of 4 with light of λ = 254 nm (pentane) yields the analogous products 20 (18%), 21 (9%), 22 (7%), and 24 (7%; s. Scheme 2). Selective ¹n, π*-excitation (λ ≥ 280 nm) of the cyclohexanone chromophore of 4 induces isomerization by cleavage of the C(δ)? O bond to give the cyclopentanones 23 (9%) and 24 (44%). Triplet-sensitization of 4 by excited acetophenone induces (E/Z)-isomerization to provide 20 (12%) and isomerization by cleavage of the C(δ)? O bond to yield 21 (26%) and 22 (20%), but no isomerization via cleavage of the C(δ)? O bond. It has been shown, that the presence of the ε;-keto group facilitates C(γ)? C(δ) bond cleavage to give a bicyclic ether 14 , but hinders the epoxy-en-carbonyl compounds 3 and 4 from undergoing cycloeliminations. The activation parameters of the valence isomerization 13 → 18 , a thermal process, have been determined in polar and non-polar solvents by analysing the ¹H-NMR. signal intensities. The rearrangement proceeds faster in polar solvents, where the entropy of activation is about ?20 e.u. Opening of the epoxide ring and formation fo the furan ring are probably concerted.     

Photochemische Reaktionen. 107. Mitteilung. Zur Photochemie offenkettiger 2,6-bzw. 2,7-Dien-Carbonylverbindungen

The Photochemistry of Open-Chained 2,6- or 2,7-Dien-Carbonyl Compounds On ¹n, π*-excitation (λ > 347 nm) citral (5) and the methyl ketone 10 isomerize to compounds A (7, 19) and B (6, 20) , whereas the phenyl ketone 11 changes into the isomer 24 of type E. Evidence is given that the conversions to A and B may arise from the ³n, π*-state of the 2,6-diene-carbonyl compounds. On ¹n, π*-excitation (λ = 254 nm) 5 and 10 yield the isomers A (7, 19) and D (18, 22) , but no products of type B. Furthermore, conversion of 10 to the isomer 21 of type C is observed. Selective ¹n, π*-excitation (λ = 254 nm) as well as selective ¹n, π*-excitation (λ > 347 nm) of the 2,7-diene-carbonyl compounds 12 and 13 give rise to isomerization to the compounds F (25, 28) , exclusively. The intramolecular [2 + 2]-photocycloadditions are shown to be triplet processes. UV.-irradiation (λ > 280 nm) of compounds F (25, 28) furnishes the isomeric products G (26, 29) which photoisomerize to oxetanes of type H (27, 30).     

Photocycloaddition of Quinoxaline-2(1H)-thiones to Alkenes

A synthetically useful C? C bond formation involving the photochemical addition of quinoxaline-2(1H)-thiones to alkenes is described. Irradiation of the quinoxaline-2(1H)-thiones 1–4 in the presence of the alkenes 7 gave the 2-(2′-mercaptoalkyl)quinoxalines 8–11 in moderate-to-good yields via ring cleavage of an intermediate aminothietane with aromatization of the quinoxaline ring. The latter was formed by [2+2] photocycloaddition of the C?S bond of the quinoxaline-2(1H)-thione and the C?C bond of the alkene.     

Photochemical Synthesis of 2-Alkylidene-4-pyrrolin-3-ones

Irradiation (λ =313 nm) of the 4-pyrrolin-3-ones 1a–1c in acetone-, 3-pentanone-and cyclopentanone solution affords the title compounds 2 , formally via H-abstrac-tion by the excited ketone and recombination of the radical pair formed.     

Photocycloaddition of Benzothiazole-2-thiones to Alkenes

The photocycloaddition of benzothiazole-2-thiones to electron-rich and aryl-substituted alkenes are described. Irradiation of N-unsubstituted benzothiazole-2-thione ( 1 ) in the presence of alkenes 3 gave 2-(2′-mercaptoalkyl)benzothiazoles 4 , and 2-substituted benzothiazoles 5 and 6 (in the case of 3a and 3h , resp.) through the ring cleavage of an intermediate 2-aminothietane (Schemes 1 and 3 ). The latter was formed by [2+2] cycloaddition of the C?S bond of 1 and the C?C bond of 3 . Irradiation of N-methylbenzothiazole-2-thione ( 2 ) and 2-methylpropene ( 3a ) gave the spiro-1,3-dithiane 8 , 1,2,6-benzodithiazocin-5-one 9 , and disulfide 10 . The structure of 9 was established by X-ray crystal-structure analysis.     

Photochemical Synthesis of 9-Methyl-tetracyclo[5.3.04,9.08,10]-decane-2,6-dione

Irradiation (λ > 340 nm) cis-8a-methyl-1,2,4a,7,8,8a-hexahydronaphthalene-2.7-dione ( 1 ) in benzene affords the title compound 2 via an intramolecular [2 + 2]-cycloaddition.     

Photochemical Reactions 150th Communication. Wavelength Dependence of the Photochemistry of 7-Methyl-β-ionone

The wavelength dependence of the photolysis of 7-methyl-β-ionone ((E)- 1 ) was investigated. Irradiation of (E)- 1 with light of λ > 347 nm leads primarily to (E/Z)-isomerization followed by transformation to the tricyclic enol ether 3 as the only secondary photoproduct. On photolysis of (E)- 1 with light of shorter wavelength (λ > 280 nm or λ = 254 nm), however, a series of other products was formed (via a) photocyclization of the dienone chromophore (→ 5 ), (b) photo-enolization (→ 8 ), and (c) a 1,5-sigmatropic H-shift (→ (E/Z)- 7 ). For the structure elucidation of the new products, 7-[¹³C]methyl-β-ionone ((E)-[7-methyl-¹³C]- 1 ) was prepared and irradiated furnishing the corresponding ¹³C-labelled photoproducts.     

13C NMR studies: XLVI—rearrangements and deuterium exchange via homoenolization in bicyclooctanones. A convenient preparation of bicyclic β,γ- and γ,δ-unsaturated ketones

With t-BuO^?/t-BuOH at 185°C bicyclo-[2.2.2] and -[3.2.1]octanones are interconvertible. In saturated systems equilibrium is attained very slowly, but in unsaturated cases an equilibrium mixture heavily favoring the [3.2.1] skeleton is obtained relatively rapidly, thereby providing a convenient route to homo and bis-homo conjugated ketones. Experiments in t-BuOD using ¹³C NMR to monitor deuterium incorporation revealed five major sites of exchange in the unsaturated ketones.     

Convenient one-pot synthesis of functionalized cyclopentene via Sm/TMSCI/t-BuOH system mediated hydrodimerization cyclization of gem-diactivated alkene

Functionalized cyclopentenes could be prepared through Sm/TMSCl/t-BuOH mediated hydrodimerization cyclization of gem-diactivated alkene in one-pot at room temperature. The trans- or trans, transform isomer is in the majority and the major product was isolated from its stereoisomers through the fractional crystallization method.     

The rate constant for the recombination of trifluoromethyl radicals at T = 296 K

The high-pressure rate constant of the CF₃ + CF₃ → C₂F₆ reaction at T = 296 K was measured in the pulse photolysis (λ = 694.3 nm, ruby laser) of CF₃NO in the presence of NO by means of the time-resolved detection of CF₃NO by the intracavity absorption of He(SINGLE BOND)Ne laser radiation (λ = 632.8 nm). The obtained value is k_2∞ = (3.9 ± 1.3) × 10⁻¹² cm³/s. © 1996 John Wiley & Sons, Inc.