Photochemische Reaktionen. 106. Mitteilung. Zur Photochemie tetraalkylsubstituierter γ-Keto-olefine

The Photochemistry of Tetraalkyl Substituted γ-Keto-olefines The photochemistry of 7,8-dihydro-β-ionone ( 1 ) in solution is shown to depend on temperature, polarity and viscosity of the solvent. UV. irradiation (λ ≥ 245 nm) in pentane at +25° converts 1 to the isomeric ethers 3 (16%), 5A (48%) and 5B (22%), whereas at ?65° 7,8-dihydro-γ-ionone ( 26 ) is obtained in 12% yield together with 13% of 3 , 12% of 5A and 9% of 5B . The ¹n,π*-excitation of 1 in acetonitrile gives similar results. In the more viscous 1,2,3-triacetoxypropane the photoisomerization 1 → 26 takes place even at + 60° (10% yield, cf. 40% at ?15°). In alcoholic solvents, however, no formation of 26 is detected, but the hitherto unknown [2+2]-photocycloaddition 1 → 11 can be observed (4% at ?7°, 15% at ?65S° in 2-propanol). An intermediate e may be involved (Scheme 14). In addition to the photoreactions 1 → 3, 5A, 5B and 11 the isomerization of 1 to the novel spirocyclic ketone 28 takes place in alcoholic solvents only. Photoisomerization 1 → 3 is presumably a photo-ene process involving a stereoselective intramolecular H-transfer. This type of photoisomerization is restricted to cyclic γ-keto-olefines. The tetraalkylated acyclic γ-keto-olefines 14 and 15 photoisomerize exclusively by [2+2]-cycloaddition, independent of the solvent. On ¹n,π*-excitation the δ,?-unsaturated bicyclic ketone 44 undergoes Norrish-Type-II photofragmentation to the diene 45 or isomerizes to the γ, ?-unsaturated ketone 17 . Competition between these two reactions is strongly temperature dependent: photolysis in pentane at ?72° yields quantitatively 45 , whereas at + 35° only 30% of 45 and 68% of 17 are obtained. UV. irradiation of the novel spirocyclic ketone 28 gives as primary photoproduct the isomeric aldehyde 29 , and in a secondary photoreaction the isomeric oxetanes 30A and 30B . Experiments with deuteriated substrates show that the isomerization of type 28 → 29 is stereocontrolled.     

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 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.     

Photochemische Reaktionen. 71. Mitteilung. Die Photoisomerisierung eines spirocyclischen α, β-Epoxyketons

On direct UV. irradiation and on triplet sensitization with acetophenone the spirocyclic epoxyketone (R)-(?)- 9 undergoes racemization (Φ^313/334 0.014, Φ^Sens 0.0060) and rearrangement to the enantiomeric spiro-β-diketones (R)-(+)- 14 (Φ^313/334 0.068, Φ^Sens 0.0037) and (S)-(?)- 14 (Φ^313/334 0.024, Φ^Sens 0.0023). The quantum yield data show that triplet reaction due to intersystem crossing is unimportant on direct irradiation, and they exclude that one common diradical intermediate of type d (Scheme 8) for the three reaction paths is involved in both the singlet and the triplet reaction. The postulate of photolytic Cα? O epoxide cleavage to intermediates of type d for the rearrangement requires that the rate of rearrangement is greater than the rate of rotation around the Cα? Cβ; bond in a given d , and that the rate difference is greater in singlet-generated d than in the triplet analogue. Reclosure of diradicals d and/or photolytic Cα? Cβ cleavage to diradical e and reclosure can account for the racemization of 9 . The optically active spiro-β-diketone 14 was found to racemize also on direct irradiation and on triplet sensitization. Furthermore, both 14 and the isomeric β-diketone 20 , which was obtained by UV. irradiation of the homocyclic epoxyketone 19 , photochemically isomerize to the enol lactones 23 and 21 , respectively.     

Photochemical reactions. 142nd communication. Photochemistry of a 6,7-epoxy-1,3-diene of the ionone series

On singlet excitation (λ = 254 nm), the epoxydiene (E)- 3 underwent (E)/(Z)-isomerization, electrocyclic ring closure of the diene side chain leading to the cyclobutenes 4A + B , and rearrangement to the cyclohexanones 5A + B . Compounds 5A + B were presumably formed in a series of processes including a 1,3-acyl shift of the homoconjugated ketone 8 , arising from (Z)- 3 by a 1,5-H-shift accompanied by cleavage of the C,O-bond of the oxirane.     

Photochemical reactions. 133rd Communication. Photochemistry of epoxydienes of the ionone series: Influence of a methyl group at the diene side chain on the oxirane cleavage

On triplet excitation (λ > 280 nm, acetone), the epoxydiene (E)- 2 undergoes (E)/(Z)-isomerization exclusively, leading to the conformers (Z)- 2A and (Z)- 2B . On singlet excitation (λ = 254 nm), apart from (Z)- 2A + B , the cyclobutenes 3A + B are formed. However, the epoxydiene (E)- 2 does not undergo reactions leading to carbene and C,O-bond cleavage products, which are normally observed on singlet and triplet excitation, respectively, of the epoxydienes of the ionone series.     

Photochemical reactions, 136th communication. Photochemistry of conjugated epoxyenones and dienes of the ionone series: Influence of a neighboring spiro-oxirane function

The preparation and photolyses of the diepoxyenones (E)- 8 and (E)- 9 as well as the diepoxydiene (E)- 10 are described. On ¹π,π^*-excitation (λ = 254 nm), the diastereoisomeric diepoxyenones (E)- 8 and (E)- 9 undergo isomerization via the ylide intermediate f and the carbene intermediate g leading to the primary photoproducts 17A and 18–21 (Scheme 8). On ¹n, π^*-excitation (λ > 347 nm), (E)- 8 shows behaviour typical of epoxyenones undergoing C(γ), O-bond cleavage of the oxirane and isomerization to compounds 22 , (E/Z)- 23 and (E)- 24 (Scheme 10). On singlet excitation, the diepoxydiene (E)- 10 , is cleaved to the carbonyl ylide j and the carbenes 1 and m (Scheme 11). The carbonyl ylide j fragments via the dipolar intermediate k to the acetylenic dienone (E)- 31 . The carbene 1 , showing behaviour typical of vinyl carbenes, furnishes the cyclopropene 30 . The alternative carbene m , however, undergoes an insertion reaction into the neighboring oxirane C,C-bond leading to the proposed but not isolated oxetene 43 , which is further transformed to the products 33A _ B by an intramolecular cycloaddition.     

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 .     

Über eine für die Invariantentheorie wichtige Funktionalgleichung

Ohne ZusammenfassungHerrnKonrad Knopp zum 60. Geburtstag am 22. Juli 1942 gewidmet     

Über das Leitvermögen binärer bzw. ternärer teilweise mischbarer Flüssigkeitsgemische mit einer zumindest schwach elektrolytischen Komponente

Ohne Zusammenfassung