The photochemistry of polymers containing anthrylmethyl vinyl ketone

The photolysis of copolymers of anthrylmethyl vinyl ketone (AMVK) with styrene and methyl methacrylate has been studied, both in solution and in the solid phase. Quantum yields of the order of 0.01 were observed in both cases for release of the major product, methyl anthracene (MA). Photolysis of an aqueous emulsion of a styrene-AMVK copolymer showed similar yields of MA. The results indicate the possibility of using the Norrish type I process as a means of releasing drugs or other biologically active compounds from polymeric matrices. © 1995 John Wiley & Sons, Inc.     

Some novel isoxazole photochemistry: A comparison with vinyl azide chemistry

Product profiles from the irradiations of 3-acetyl-5-methylisoxazole (4) and Z-3-azido-3-hexene-2,5-dione (5) were compared. Whereas both compounds gave rise to azirine 7, diacetylacetonitrile (6) was produced only from (4).     

Aza-Baylis-Hillman reaction of salicyl N-tosylimines with methyl vinyl ketone, ethyl vinyl ketone or phenyl vinyl ketone

Reactions of salicyl N-tosylimines with methyl vinyl ketone, ethyl vinyl ketone or phenyl vinyl ketone proceeded smoothly under mild conditions to give the corresponding chromanes or aza-Baylis-Hillman adducts in moderate to excellent yields in the presence of phosphine or nitrogen Lewis base.     

Approaches to open fullerenes: synthesis and kinetic stability of diels-alder adducts of substituted isobenzofurans and C60

We have examined the reactions of 1,3-disubstituted isobenzofurans with the fullerene C60 in the context of an approach to open a large orifice on the fullerene framework. A variety of substituted isobenzofurans (6a-h), generated from the reaction of 1,4-substituted 1,4-epoxynaphthalenes 3a-h with 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine (4a) or 1,2,4,5-tetrazine (4b), were added to C60 to afford the Diels-Alder adducts 7a-h. The thermal stability of these adducts toward retro-Diels-Alder fragmentation differs greatly in solution from that in the solid state. In solution, the relatively facile retro-Diels-Alder fragmentation of monoadducts 7a and 7c, to give C60 and the free isobenzofurans 6a and 6c, have rate constants (and activation barriers) of k=9.29x10(-5) s-1 at 70 degrees C (Ea=32.6 kcal mol-1) and k=1.36x10(-4) s-1 at 40 degrees C (Ea=33.7 kcal mol-1), respectively, indicating that the addition of isobenzofurans to C60 is readily reversible at those temperatures. In the solid state, thermogravimetric analysis of adduct 7a indicates that its decomposition occurs only within the temperature range of 220-300 degrees C. As a result, these compounds can be stored at room temperature in the solid state for several weeks without significant decomposition but have to be handled within several hours in solution.     

Diastereoselective diels-alder reactions of optically-active vinyl sulphoxides

The Diels-Alder reaction of an optically active vinyl sulphoxide containing a second electron withdrawing group with cyclopentadiene gave separable diastereomers. The effect of Lewis acid catalysis on the reaction was studied. Reaction of an acetylenic anion with menthyl p-toluene sulphinate gave an anomalous product.     

The solution photochemistry of substituted cycloheptatrienes

The solution photochemistry of several ethoxycarbonyl- and ethoxycarbonyl-methoxy-substituted cycloheptatrienes has been investigated. The results have been used to analyse the directional specificity of ring-closure and 1,7-hydrogen migration reactions. This specificity is interpreted in terms of polarisation within the S₁ state which undergoes either (a) allowed photochemical reactions to give the observed products directly or (b) isomerisation to a trans, cis, cis-cyclohepatriene which then reacts via allowed ground-state processes. In at least two instances the directional specificity of the ring-closure reaction is wavelength dependent and this is attributed to the differing reactivities of the S₁ and S₂ states.     

Cope rearrangements of diels-alder adducts containing norbornene and norbornenone systems

The product formed from cyclopentadiene and the cyclo-octatetraene dimer 5a has been shown to possess structure 6a, probably resulting from Cope rearrangement of an initial adduct 4a. The reaction of tetraphenylcyclopentadienone with 1 - methoxybuta - 1,3 - diene yields a mixture of the exo-adduct 14 and the rearranged endo-adduct 13 Rearrangement of the norbornenone derivative 27 gives the Cope product 29 Treatment of the 4,5-fused 2,3,4,5-tetrachlorocyclopent-2-enones 29,40 and 41 with powdered sodium hydroxide in tetrahydrofuran results in ring-cleaveage with the formation of 2,3,5-trichlorobuta-2,4-dienoic acid derivatives, 36, 43 and 44 respectively.     

O-nitrobenzyl photochemistry: Solution vs. solid-state behavior

The efficiency of various 2-nitrobenzyl groups in the photogeneration of carboxylic acid from nitrobenzyl esters has been determined, and the solution vs. solid polymer matrix photochemistry is compared. Generally, the quantum yield for photoreaction is lower in the solid state, probably due to decreased conformational mobility. The substitution that affords the largest increase in quantum yield (?) is at the α-carbon atom. The value of ? for α-methyl-2-nitrobenzyl trimethylacetate in solution is 0.65 vs. 0.13 for the parent 2-nitrobenzyl ester.     

Facile retro diels-alder reaction of a vinyl lithium compound

Attempts to generate benzobarrelyne 8 by loss of lithium chloride from 4 resulted in a facile retro Diels-Alder reaction of the “dimeric” adduct formed by addition of 4 to 8.     

Unexpected solid-state photochemistry of an alpha-thiophenyl-alpha'-thiophenyl-S,S-dioxo-substituted ketone

Samples of 2,4-dimethyl-2-(thiophen-3-yl)-4-(thiophen-3-yl-S,S-dioxo)pentan-3-one 2 were obtained by controlled MCPBA oxidation of 2,4-dimethyl-2,4-di(thiophen-3-yl)pentan-3-one 1. Rather than the expected photodecarbonylation, UV--vis irradiation of 2 led to the intramolecular 2 + 2 photocycloaddition product 5 in quantitative yields (by GC and NMR) both in solution and in crystalline solid state. Detailed X-ray powder diffraction analyses revealed that the solid-state reaction of sulfone 2 occurs with a loss of long-range order despite retaining some birefringence under polarized microscopy.     

Intramolecular diels-alder reactions. XI. Modal selectivity in the syntheses of some parent cyclolignan lactones

Ph(C₂)CH₂Cl and Ph(C₂)'CO₂Na [where (C₂) = -C=C- or trans-CH=CH-, (C₂)' = -C=C- or cis-CH=CH-] reacted in refluxing dimethylformamide to yield unsaturated esters Ph(C₂)'CO₂-CH₂(C₂)Ph and/or their intramolecular Diels-Alder cyclization products (cyclolignan lactones). It was found that modal selectivity for cyclization in DMF sometimes varies from that found previously with acetic anhydride as solvent. Two new parent tetrahydrocyclolignan lactones were synthesized.     

Influence of the β-substitution on the photochemistry of α,2-diacetoxystyrenes. Irradiation of phenyl,vinyl, and benzyl derivatives

Summary -Substitution shows a pronounced influence on the photochemistry of ,2-diacetoxystyrenes. As in the case of the parent compound, intramolecular cyclization with participation of the neighbouring 2-acetoxy group takes place upon irradiation of the enol esters4a–c; however other processes are also observed, depending on the substrate. The phenyl derivative4a gives theE isomer7a and the phenanthrene9. The vinyl derivative4b also undergoescis-trans isomerization and/or photooxidation, to afford7b and10. Finally, a 1,4-acyl migration occurs in the benzyl derivative4c, whereby the 1,4-diketone12 is formed.

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Einfluß der -Substitution auf die Photochemie von ,2-Diacetoxystyrolen. Bestrahlung von Phenyl-, Vinyl- und Benzylderivaten

Zusammenfassung Bei ,2-Diacetoxystyrolen haben die -Substituenten einen deutlichen Einfluß auf das photochemische Verhalten. Wie im Fall der Stammverbindung erfolgt bei der Bestrahlung der Enolester4a–c intramoleukulare Cyclisierung unter Einbeziehung der benachbarten 2-Acetoxygruppe; jedoch werden je nach Substrat auch andere Reaktionen beobachtet. Das Phenylderivat4a liefert dasE-Isomer7a und das Phenanthren9. Das Vinylderivat4b erfährt ebenfallscis/trans-Isomerisierung zu7b und/oder Photooxidation zu10. Beim Benzylderivat4c tritt eine 1,4-Acylverschiebung zum 1,4-Diketon12 auf.

     

Aza-Morita-Baylis-Hillman reaction of ethyl (arylimino)acetate with methyl vinyl ketone and ethyl vinyl ketone

Aza-Morita-Baylis-Hillman (aza-MBH) reaction of ethyl (arylimino)acetate with methyl vinyl ketone and ethyl vinyl ketone has been investigated. We found that aza-MBH adducts 1 could be formed in the presence of DABCO (30 mol %) and the corresponding adducts 2 could be obtained in the presence of PPh₃ (30 mol %) in moderate to good yields in acetonitrile under mild conditions, respectively.     

Properties and cage lactone synthesis of diels-alder adducts from 2-pyrones

New cage lactones were synthesized by the photocyclization of the tricyclodienolactones 1a, 1b, 2 which were available from the Diels-Alder reactions of 2-pyrones with p-benzoquinones or norbornadiene. Retro-Diels-Alder reactions of cross-adducts between 2-pyrone-mono-adducts and p-benzoquinone were also described.     

Laser photochemistry of aromatic substituted cyclobutanes and cyclobutenes

The photochemical ring opening and ring cleavage reactions of 6b,8a-dihydrocyclobut[a]acenaphthylene (1) and two similar compounds are described. These reactions occur at room temperature only if the irradiating light intensity is greater than MW/cm², easily obtained with excimer and dye lasers. This is rationalized in terms of a consecutive two-photon absorption to reach higher-lying reactive states. The mechanism proposed for the reaction of 1 also describes the product distribution, which depends on irradiation parameters such as laser pulse length, wavelength, intensity, and oxygen content of the solvent.     

Reactions of 2-aminooxazoles and 2-aminothiazoles with dienophiles. Isolation of stable diels-alder adducts

Room temperature reaction of 2-aminooxazole 1 and its 4- and 4,5-substituted derivatives, with dimethyl acetylenedicarboxylate gave good yields of Diels-Alder adducts 2 , isolated as stable crystalline compounds. A competing process produced oxazole[3,2-a]pyrimidines 3 , also in good yield. Minor products were also identified. 2-Amino-4-methylthiazole ( 6 ) reacted in a similar manner and gave the Diels-Alder adduct 7 and a thia-zolo[3,2-a]pyrimidine 8 as main products with a lesser amount of a thiazole [3,2-d][1:3]diazepine ( 9 ). The aminooxazoles reacted with olefinic dienophiles to give pyridine derivative, formed by breakdown of the original unstable adducts.