Photochemische Reaktionen. 90. Mitteilung. Die UV.-Bestrahlung von (E)-5-Isopropyl-6-methyl-5,6-epoxy-hept-3-en-2-on

Photolysis of (E)-5-Isopropyl-6-methyl-5,6-epoxy-hept-3-en-2-on. This paper continues the series of investigations of the photochemistry of α, β-unsaturated γ, δ-epoxy-ketones, by examinating the photochemical behaviour of the aliphatic vinylogous epoxy-ketone 1 , the chromophore of which is structurally similar to that of γ, δ-epoxy-(E),β-ionone ( 44 ). On π, π*-excitation (λ = 254 nm) 1 isomerizes mainly to the enol-ether 2 and gives as minor products the isomeric dihydrofurane 3 , the 1,5-diketones 4 and 5 and the 1,3-diketone 6 . To a smaller extent, 1 also undergoes photofragmentation to the furane 7 , the allenyl-ketone 8 and the cyclopropenyl-ketone 9 . On n,π*-excitation (λ ≥ = 347 nm) 1 yields the photoisomers 3 , 4 , 5 and in traces the hydroxyallenyl-ketone 14 , but no fragmentation products. It is shown that on irradiation at λ ≥ = 254 nm the 1,5-diketone 4 isomerizes to 5 , 6 and 15 and photodecarbonylates to the β, γ-unsaturated ketone 16 . The isomers 3 , 4 and 5 , obtained both from n, π*- and π,π*-excitation, represent products of cleavage of the C(γ)? O-bond in 1 . The enolether 2 , on the other hand, formed only by π,π*-excitation, results from cleavage of the C(γ)? C(δ)-bond. Finally, the fragmentation products 7 , 8 and 9 , which could be detected only on π,π*-excitation, may arise from a common intermediate g ? h .     

Photochemische Reaktionen. 95. Mitteilung. Zur Photochemie konjugierter Epoxy-enone: Die UV.-Bestrahlung von 9-Isopropyl-6-methyl-9, 10-epoxybicyclo [4.4.0] dec-1-en-3-on

The Photochemistry of Conjugated Epoxy-enones: Photolysis of 9-Isopropyl-6-methyl-9,10-epoxybicyclo [4.4.0]dec-l-en-3-on The title compound 1 undergoes on π, π*-excitation vinylogous β-cleavage of the C(γ), O-bond and isomerizes to the unsaturated 1, 5-diketone 8 (58%) and the tricyclic diketone 9 (14%). On n, π*-excitation, however, 1 undergoes only desoxygenation to the dienone 7 (ca. 15%) besides polymerization. UV.-irradiation of 1 (λ ≥ 347 nm) in the presence of tributyl-stannane gives 7 in 85% yield; in the presence of tributylstannane-d₁ 1 yields 13 , the deuterated analogon of 7 (85% yield; d₁ ca. 50%); 7 has been proven to be stable on π, π* - as well as on n, π*-excitation.     

Photochemische Reaktionen. 109. Mitteilung [1]. Zur Photochemie konjugierter δ-Keto-enone und β,γ,δ,ϵ-ungesättigter Ketone

Photochemistry of Conjugated δ-Keto-enones and β,γ,δ,?-Unsaturated Ketones On ¹π,π*-excitation the δ-keto-enones 5–8 are isomerized to compounds B ( 18 , 22 , 26 , 28 ) via 1,3-acyl shift and to compounds C ( 19 , 23 , 27 , 29 ) via 1,2-acyl shift, whereas the β,γ,δ,?-unsaturated ketone 9 gives the isomers 32 and 33 by 1,2-and 1,5-acyl shift, respectively. Furthermore, isomerization of 6 to 24 , dimerization of 8 to 30 and addition of methanol to 8 ( 8 → 31 ) is observed. Unlike 7 and 8 the acyclic ketones 5 , 6 and 9 undergo photodecarbonylation on ¹π,π*-excitation ( 5 → 20 , 21 ; 6 → 20 , 25 ; (E)- 9 → 35–38 ). Evidence is given, that the conversion to B as well as the photodecarbonylation of 5,6 and 9 arise from an excited singulet state, but the conversion to C as well as the dimerization of 8 from the T₁-state.     

Photochemische Reaktionen 115. Mitteilung [1]. Zur Photochemie konjugierter γ,δ-Epoxyenone: Der Einfluss eines Hydroxylsubstituenten in ϵ-Stellung

Photochemistry of Conjugated γ,δ-Epoxyenones: The Influence of a Hydroxy Substituent in ?-Position On ¹n, π*- or ¹π,π*-excitation (λ ≥ 347 or λ=254 nm), the ?-hydroxy-γ;,δ-epoxyenone 8 undergoes fission of the C(γ)? O bond followed by the cleavage of the C(δ)-C(?) bond. This hitherto unknown sequence of reactions is evidenced by the structure determination of the new type products 10–17 and 25 , including a synthetic proof for 12 and the X-ray analysis of 11 (X-ray data: triclinic P1; a=7,386(2), b=8,904(4), c=9,684(5)Å; α=82,29(4)°, β=74,46(3)°, γ=82,29(3)°; Z=2). The selective ¹π,π*-excitation also induces competitive C(γ)-C(δ) bond cleavage to yield the bicyclic acetal 18 and a ketonium-ylide intermediate a , which photochemically forms a carbene b giving the allene 19 and the cyclopropene 20 . On ¹n,π*-excitation of the acetate 9 the initial C(γ)-O bond fission is, in contrast to the behaviour of the corresponding alcohol 8 , followed by a 1,2-methyl shift affording (E/Z)- 28 or by a cyclization-autoxidation process yielding the lactone 29 .     

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.     

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. 85. Mitteilung [1]. Zur Photochemie von α, β-Epoxy-eucarvon

Photochemistry of α,β-epoxy-eucarvone . On π,π^*-excitation (λ = 254 nm) 4 isomerizes to the bicyclic ketoaldehyde 5 ; on n,π^*-excitation (λ ? 280 nm) 4 gives 5 , the β,γ-unsaturated ketone 6 , the enone 7 and the cyclobutanone 8 . Scission of the (C—C)-bond of the oxirane 4 would give the dihydrofurane e , which could isomerize to the ketoaldehyde 5 . On the other hand, 4 is assumed to isomerize to the β,γ-unsaturated aldehyde c , which could yield 6 and 7 by photodecarbonylation. The cyclo-butanone 8 is shown to be a photoisomer of the ketone 6 . Furthermore, eucarvol ( 18 ) rearranges by a thermal [1,5]-H-shift to dihydro-eucarvone ( 20 ); on UV.-irradiation 18 gives the bicyclic isomers 27 and 28 .     

Photochemische Reaktionen. 51. Mitteilung [1]. Zur Photochemie von gesättigten β-Ketosulfiden III. Strukturaufklärung eines weiteren Photoproduktes Zusammenfassende Beurteilung des photochemischen Reaktionsbildes

Ultraviolet irradiation of the saturated β-ketosulfide 2 [(charge-transfer)- or (n → π*)-excitation] in methanol or benzene solutions resulted in the formation of the products 4, 5a, 6 (due to α-cleavage) and 7 [due to (C_α–S)-fission]. Compounds 4, 6 and 7 have been described earlier [1] [2]. The structure elucidation of 5a is reported in this paper. The photochemistry of the β-ketosulfide 2 is summarized.     

Photochemische Reaktionen. 50. Mitteilung [1]. Zur Photochemie von gesättigten β-Ketosulfiden II. Synthese von 6-Hydroxy-2-thia-7-oxa-isotwistan

The results of the ultraviolet irradiation of the saturated β-ketosulfide 2 are discussed. The photochemistry of 2 is characterized by the occurrence of two primary photoprocesses. Their efficiences depend markedly on the excited transition, (charge-transfer)- or (n → π*)-excitation, respectively. In methanol solution (charge-transfer)-excitation leads almost exclusively to product 7 , due to (C_α – S)-fission, and (n → π*)-excitation to nearly equal amounts of 7 and of products 4 and 6 which result from α-cleavage. On solvent sensibilization in benzene products 4, 6, 7 and the still unidentified product 5 ² are formed. Compounds 4 and 6 have been described earlier [2]. The structure elucidation of 7 is reported in this paper. Acid-induced transformation of 7 yields the dihetero-isotwistane 15 .     

Photochemical Reactions 127th CommunicationPhotochemistry of Epoxy-enones: Intramolecular Trapping of a Carbonyl Ylide

On ¹n, π* -excitation 5, 6-epoxy-2-hydroxy-5, 6-dihydro-β-ionone ((E)-4) shows the typical behaviour of a, β-unsaturated γ, δ-epoxy ketones undergoing primarily C(γ), O-cleavage of the oxiran. However, ¹π, π*-excitation of (E)? 4 leads to enol ether 10 which is formed by intramolecular insertion of the hydroxyl group of the ylide c .     

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.     

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).     

Photochemische Reaktionen. 116. Mitteilung [1]. Notiz zur 1γ, δ*-induzierten Photospaltung von γ, δ-Epoxy-eucarvon

π, π*-Induced Photocleavage of γ, δ-Epoxy-eucarvone . On ¹π, π*-excitation 1 undergoes cleavage of the C, C-oxirane bond ( 1 → c ) and isomerizes to the bicyclic dihydrofurane compound 5 . In addition, 1 shows photocleavage of the C (γ), O-oxirane bond ( 1 → d ) and gives the isomers 2, 3, 6, 7 and 8. Furthermore, the cyclohexenone 9 and the cyclohexene-1, 4-dione 10 are formed presumably via an intermediate 13 , which could also arise from d. Besides these products the compounds 11 and 12 are obtained, which are photoproducts of 2 .     

Photochemische Reaktionen. 93. Mitteilung. Zur Photochemie konjugierter Epoxy-inone: Die UV.-Bestrahlung von 5,6-Epoxy-5-isopropyl-6-methyl-hept-3-in-2-on

The Photochemistry of Conjugated Epoxy-Inones: Photolysis of 5,6-Epoxy-5-isopropyl-6-methyl-hept-3-in-2-on This paper continues the series of investigations of the photochemistry of α,β-unsaturated γ,δ-epoxyketones by examining the hitherto unknown photochemical behaviour of α,β-acetylenic-γ,δ-epoxy-ketones. As model compound, the aliphatic epoxy-ynone 7 (thermally stable at 180°) was synthesized (Scheme 1). It can be converted with BF₃O (C₂H₅)₂ in good yields to the 1,5-diketone 8 , the yne-1,4-diketone 49 and in small amounts to the fluorhydrine 50 (Scheme 1). On n,π*- or π, π*-excitation, 7 shows mainly cleavage of the C (γ)-O-bond to give a diradical a (Scheme 11), whose ultimate fate is strongly solvent dependent. In acetonitrile a mainly rearranges to the 1,5-diketone 8 and, to a smaller extent, shows fragmentation to acetone and formation of polymers. Except for small amounts of the dimeric products 9A,9B and biphenyl, the same compounds are obtained in benzene. In cyclopentane, however, a gives only little of 8 , and mainly a plethora of compounds formed by a radical process like H-abstraction from solvent, incorporation of cyclopentylradicals, dimerization and fragmentation reactions (9A, 9B, 11–20) (Scheme 3). Irradiation of 7 in propan-2-ol or in dioxane yields products of analogous radical processes as well of photoreduction (Scheme 4). However, the analogous epoxyenone 32 gives mainly products of photoisomerizations without interference by the solvent [6]. On photochemical excitation in acetonitrile, the 1,5-diketone 8 shows unspecific decomposition, but in cyclopentane it yields the reduction products 12, 26A, 26B, 27, 28 plus cyclopentylcyclopentane (15) (Scheme 6).     

Photochemical reactions. 132nd communication. Photochemistry of 5,6-epoxy-5,6-dihydro-7-methyl-β-ionine: Influence of a methyl group at the enone side chain on the oxirane cleavage

¹n, π*-Excitation of the γ,δ-epoxy-enone (E)- 3 leads exclusively to the conformers (Z)- 3A + B . On ¹π, π*-excitation of (E)- 3 , in addition to (Z)- 3A + B , products 6–9 arising from a carbene intermediate e are formed. However, products of an isomerization via C(γ), O-bond cleavage of the oxirane were not formed on either mode of excitation. On thermolysis, at 80° the conformer (Z)- 3A is transformed into (Z)- 3B , which on photolysis returns to (Z)- 3A and (E) -3 . At 160°, however, (Z) -3B rearranges to the isomers 6, 10 and 11 .     

Photochemische Reaktionen 113. Mitteilung [1]. Zur Photospaltung konjugierter γ, δ-Epoxyenone: UV.-Bestrahlung von 5, 6-Epoxy-3,4-didehydro-5,6-dihydro-β-jonon

The Photoinduced Cleavage of Conjugated γ, δ-Epoxyenones: UV.-Irradiation of 5,6-Epoxy-3, 4-didehydro-5,6-dihydro-β-ionone On ¹n, π*-excitation (λ ≥ 347 nm) in pentane or CClF₂CFCl₂ (E)- 1 is isomerized to the dihydrofurane (E/Z)- 2 as well to the ethers 3 and 5. Besides these products the isomeric cyclopropane derivative (E)- 4 and the acetal 6 are obtained in methanol. The detection of 6 indicates the formation of an intermediate ketoniumylide a which may give 6 by addition of methanol. ? On ¹π, π*-excitation (λ=254 nm) in acetonitrile-d₃, CClF₂CFCl₂ or pentane (E)- 1 yields almost exclusively (E)- 2. In methanol 6 is obtained in addition to (E/Z)- 2 , but no (E)- 4 and 5 is formed.     

Photochemische Reaktionen. 104. Mitteilung [1]. Zur Photospaltung der C,C-Oxiranbindung konjugierter γ, δ-Epoxy-enone: Photolyse von 4-Methyliden-5,6-epoxy-5,6-dihydro-β-jonon

The photoinduced cleavage of the C,C-oxirane bond of γ, δ-epoxy-enones: UV.-irradiation of 4-methylidene-5,6-epoxy-5,6-dihydro-β-ionone On ¹n, π*-excitation (λ ≥ 347 nm, pentane) 5 gives the isomeric bicyclic ether 10 in 75% yield (s. Scheme 2). In methanol the photoconversion of 5 to 10 is strongly reduced (12%) in favour of the formation of the methanol adduct 11 (43%). On photolysis in aqueous acetonitrile 5 is converted to the bicyclic ether 10 (9%), the dihydrofurane 12 (18%) as well as to the triketones 13A and 13B (7%), and 14 (23%). On ¹π, π*-excitation (λ = 254 nm) in pentane no 10 is formed, but 5 isomerizes to the tricyclic cyclopropyl compound 16 (59%), the allenic product 17 (10%), and the cyclopropene compound 18 (12%; s. Scheme 3). Photolysis in methanol furnishes 11 (63%), and 18 (4%), but no tricyclic cyclopropyl compound 16 . In a secondary photoreaction (λ = 254 nm) the dihydrofurane 12 is isomerized to the bicyclic cyclopropyl compound 20 . Evidence is given that the products 11 and 13 are formed by solvent addition to an intermediate ketonium ylide b (s. Scheme 12). The presence of b is further proven by the formation of 12 , a product of an electrocyclization of b . On photofragmentation of b carbenoids d and e are presumably formed (s. Scheme 14). 1,2-Hydrogen shift in d yields the allene derivative 17 , and cyclization of d gives the cyclopropene compound 18 . On the other hand, e cyclizes to the non isolated cyclopropene compound 69 which is transformed to 16 by an intramolecular [4 + 2]-cycloaddition. The present investigation shows that the photochemistry of 5 is determined by photoinduced C,C-bond cleavage of the oxirane ring. This is in sharp contrast to the photochemistry of conjugated γ, δ-epoxy-enones without the additional double bond in ε, ζ-position, where selective photocleavage of the C(λ), O-bond is observed.     

n→π*-Übergänge in Dicarbonylverbindungen Der Einfluss der n,n- und π*, π*-Wechselwirkung

By CNDO-CI calculations we have found that dicarbonyl compounds exhibit only two n → π* transitions in the visible or near UV. region, instead of four as expected from simpler MO-models. The dominant features of the long-wavelength electronic spectra may be characterized by the relative energy of the two n and the two lowest π* orbitals. In general we distinguish between three cases:

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Photochemical reactions. 147th Communication. Further investigation of the photochemistry of 5,6-epoxy-5,6-dihydro-β-ionone: Product formation via a carbonyl-ylide intermediate

On π,π*-excitation of the epoxyenone (E)- 1 (λ = 254 nm, MeCN), in addition to the previously isolated compounds 2 – 9 , the new products 10 – 12 , derived from the ylide intermediate c were isolated. Further evidence for the ylide c was obtained by the rapid racemization of the optically active epoxyenone (?)-(E)- 1 .     

Photochemische Reaktionen 122. Mitteilung [1]. Zur vinylogen β-spaltung von epoxy-enonen: Photoisomerisierung des 3,4:5,6-diepoxy-5,6-dihydro-β-jonons

Vinylogous β-Cleavage of Epoxy-enones: Photoisomerization of 3,4: 5,6-Diepoxy-5,6-dihydro-β-ionone On ¹n,π*-excitation (λ>347 nm), 3,4:5,6-diepoxy-5,6-dihydro-β-ionone ((E)- 3 ) shows the typical behaviour of α,β-unsaturated γ,δ-epoxy ketones furnishing the (Z)-enone 3 and by C(γ),O cleavage of the oxirane the dihydrofuryl ketone 10 and the cyclohexanones (E/Z)- 11 . However, on ¹π,π*-excitation an unexpected type of transformation is observed: (E)- 3 is isomerized to the four aliphatic triketones 5 – 8 as the main products. To a smaller extent the allene diketone 9 is formed by a known type of isomerization as well as (Z)- 3 . As the starting material for the preparation of (E)- 3 , the known epidioxy-enone (E)- 4 was used. In addition to (E)- 3 , (E)- 4 gives the aliphatic triketone 6 and the hydroxyenone 15 by thermal or catalytic isomerization.