Photochemical coupling between halogenoheterocyclic and heterocyclic derivatives (original) (raw)
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The Journal of Organic Chemistry, 1995
Parameters useful to predict reactivity and regiochemical control of photocoupling reactions between haloheterocyclic derivatives and arylalkenes or arylalkynes have been studied. Electrochemical properties of arylalkenes and arylalkynes are shown to be useful to predict the reactivity of the substrates. However, oxidation potentials fail as reactivity indices if very fast photochemical processes are in competition with the observed complex formation between substrates and halogen atoms. The regiochemical behavior of the reaction can be estimated on the basis of dipoles of the reagents. In this case the assumptions that a reagent approaches the other on parallel planes and that the prevalent interaction is between the SOMO of the radical and the LUMO of the other reagent have been accepted.
Gazzetta chimica Italiana
Quantum yields for 14 and 17 were determined in a similar way with 4 as an actinometer: dZMnm(-14) = 0.0.0094 f 0.001; Flash Photolysis Experiments. Triplet absorption spectra were obtained at 25 "C on -3 mL of acetonitrile solutions of 5 (0.0087 M) and 14 (0.010 M) and benzophenone (0.005 M) that were thoroughly purged with argon. Benzophenone triplet decay (2.78 X 105 s-l) was monitored at 480 nm. The absorption spectra were generated by measuring absorbances at 5-nm intervals in the range 290-580 nm. Because of photochemical instability, the triplet absorption spectrum of isoxazole 5 was a composite of measurements taken from different samples. In addition, the spectrum was recorded in both sweep directions in which case ~3000m(-17) = 0.083 f 0.004. small differences in optical densities were observed. Both compounds had a strong absorption peak at ca. 320 nm, and in addition, 5 showed a broad maximum at 480 nm and 14 showed a shoulder a t 410 nm. The transient lifetimes in the absence of biphenyl were 276 and 48 ns, respectively. In the presence of 0.01 M biphenyl a new absorption appeared at 360-365 nm. Quenching rates were calculated from lifetime measurements in the presence and absence of biphenyl: 5, 8.3 X lo8 M-ls-l; 14, 2.0 X lo9 M-' S-1.
The Journal of Organic Chemistry, 1990
Quantum yields for 14 and 17 were determined in a similar way with 4 as an actinometer: dZMnm(-14) = 0.0.0094 f 0.001; Flash Photolysis Experiments. Triplet absorption spectra were obtained at 25 "C on -3 mL of acetonitrile solutions of 5 (0.0087 M) and 14 (0.010 M) and benzophenone (0.005 M) that were thoroughly purged with argon. Benzophenone triplet decay (2.78 X 105 s-l) was monitored at 480 nm. The absorption spectra were generated by measuring absorbances at 5-nm intervals in the range 290-580 nm. Because of photochemical instability, the triplet absorption spectrum of isoxazole 5 was a composite of measurements taken from different samples. In addition, the spectrum was recorded in both sweep directions in which case ~3000m(-17) = 0.083 f 0.004. small differences in optical densities were observed. Both compounds had a strong absorption peak at ca. 320 nm, and in addition, 5 showed a broad maximum at 480 nm and 14 showed a shoulder a t 410 nm. The transient lifetimes in the absence of biphenyl were 276 and 48 ns, respectively. In the presence of 0.01 M biphenyl a new absorption appeared at 360-365 nm. Quenching rates were calculated from lifetime measurements in the presence and absence of biphenyl: 5, 8.3 X lo8 M-ls-l; 14, 2.0 X lo9 M-' S-1.
Journal of the American Chemical Society, 1989
Photoexcitations of 2-allyl-1-naphthol and 1-allyl-2-naphthol caused cyclization, forming dihydrofuranyl and pyranyl ethers and the secondary photodehydrogenation of the dihydrofuranyl ethers. The quenching experiments of the product formations as well as fluorescence intensities of allylnaphthols by methanol, triethylamine, N-nitrosodimethylamine, and 1,3-dienes confirmed that the cyclization occurred from the singlet excited-state proton transfer (ESPT) of the phenolic group; Le., kinetic acidity initiated photocyclization. The primary photoprocess is quenched mainly by a static quenching process arising from the ground-state hydrogen-bonding association between allylnaphthols and a quencher, as supported by IR spectroscopy, and to a minor extent by a dynamic quenching of the singlet excited state of the allylnaphthol intramolecular proton-transfer complexes. Kinetic analyses also reveal the presence of two identifiable intramolecular ESPT intermediates, probably conformers of the proton-transfer species; one is the precursor of the furanyl ethers and not quenchable in the dynamic process by Et,N, and the other that of the pyranyl ethers and quenchable in the dynamic process by Et,N. The IR absorption of intramolecular hydrogen bonds between the OH and olefin groups began to be replaced by that of intermolecular hydrogen bonds at tetrahydrofuran concentrations
Tetrahedron, 2002
Photochemistry of o-allyloxy-/crotyloxyacetophenones (6a,b) has been investigated under different conditions. Irradiation of 6a,b in dry benzene, under N 2 atmosphere (Pyrex filter), led to the isolation of (syn)-2-ethenyl/propenyl-3-hydroxy-3-methyl-2,3dihydrobenzofurans (7a,b,10%) as the sole product. Irradiation of 6a,b in dry benzene in the presence of 0.1-0.4 mol equiv. of triethylamine resulted in slightly increased formation of 7a,b, besides pinacols (9 and 10) and triethylamine addition products (11 and 12). However, the formation of 7a,b is suppressed with increasing molar ratios of triethylamine, with increased formation of products (9-13). On the other hand, irradiation of 6a,b in dry acetonitrile results in the formation of both syn-(7a,b) as well as anti-isomers of benzodihydrofuranols (8a,b), besides some highly unexpected intramolecular arene-olefin addition products (14-16); formation of these intramolecular arene-olefin addition products is quenched in the presence of 0.1 mol equiv. of triethylamine. With increasing molar ratios of triethylamine, in acetonitrile solvent, the formation of 7, 8 is also suppressed with increased formation of products (9-13) derived from photoreduction of carbonyl function through electron transfer from TEA. No product derived from intramolecular interaction of the ketone derived anion radical/ketyl radical with an olefinic moiety has been detected. A plausible mechanistic rationalization of the results obtained is presented.
Tetrahedron, 1981
AMruGThe phototeactiom of knzene. tducne. anisok. and knzonitrik with acrylonilrik. merhacrybnitrik. sod vinyl acetak. and of 104ucnc and o-ad p-xylm with makic anhydride are dcscrikd. Tk acrybniuiks do DoI react with knzoniwik but ykhf mixtures of ortho photocycbaddwts with the other arenes. Cootnry to previous &I& holb cxo and cndo s~ereoisomers of tk orrho cycbadducts of knzcm and acrybr&ik are formed: I& reaction is sekctivc towards tk cxo komtr hut tht stereoisomers from mcthacrybnifrik ad knzene are formed with approximately equal efficiencies. Compkx mixtures of rcgio-ad skrcoisomers of the o&o cycbadducts are formed klwecn tolucnc and tk acrybnitriks bum tkir addition 10 anisok is more sekctivc and in acetoait& cssentiy only I&attack of tk ctbykne on Ibe arely is observed. The 2: I photoadducts of makic anhydride with tohrene and o-rod p-xykne refkct formation of two regio orrho photocycbxlducts in each case. The variation in the ratios of &se isomers with temperature and light intensity is interpreted io terms of the d&k photolabilitks of tbc I : I adducts and tkir reactivilics towards cbt thermal ddbioa of the & q okcuk of makic arthybride. Vinyl acelate undergoes 13cydoadditioa to knr.onitrik buf with tbc otkr arenes. metu cycbadduc~~ are favourtd. lkse latter addirious are specifially 2.6 with respect (0 tobew and an&k but there is littk ngbsekdvity with respect (0 th e&ykne atOut& tk Lendo acetate of Ibe mtfa cycbddwr with knxeoe dm coostirute 60% of tk reaction mixture.
J Am Chem Soc, 1968
The photochemical rearrangement of 4,4-diphenylcyclohexenone (1) to cis-and rrans-5,6-diphenylbicyclo[3.1 .O]hexan-2-one (2) and 3,4-diphenylcyclohex-2-en-lone (3) has been studied in further mechanistic detail. Remarkably, over a 100-nm wavelength range the quantum yield of the major reaction product was unchanged and the "excited-state fingerprint" proved insensitive to wavelength. From this it was concluded that initial excess vibrational energy of the excited state is very quickly dissipated to solvent and that intersystem crossing occurs to the same triplet excited state independent of the configuration of the singlet initially produced. In contrast to wavelength insensitivity, a dramatic dependence on reaction temperature was encountered. This was shown not to be due to viscosity effects, for the intramolecular rearrangement rate was noted to be viscosity independent. A 50" temperature increase was found to increase the quantum yield of phenyl migration approximately 6-fold. This temperature increase led to a ca. 16-fold rate enhancement for triplet rearrangement and only a ca. 2-fold increase in rate of triplet decay. It was concluded that an activation energy of about 10 kcalimol is required for rearrangement of the excited triplet of 4,4-diphenylcyclohexenone (1). The frequency factors were 10l3-1O i3. Evidence was uncovered indicating that the stereoselectivity arises only partially from a concerted pathway being energetically favored and mainly from an entropy effect favoring the concerted process. From this study it is concluded that excited-state potential energy surfaces show thermal activation barriers similar to those encountered in ground-state chemistry. Additionally, frequency factors of the same order of magnitude as in ground-state reactions, when encountered, point to excited-state transformations with molecular demands similar to those imposed in ground-state reactions. These aspects and other details of the reaction mechanism are discussed. 0.0006. cis-5,6-Diphenylbicyclo[3.l.0]hexan-2-one (504.2 mg, 2030 pmol) x 10-5. pmol produced, 9 = 6 X x 10-4. Run 20. added to 14C photolysate (46.07 mg, 185.5 pmol): (18), 41 mg, 113-114", 2.930 =t 0.021, 0.0625 pmol produced, 9 = (9.1 f 2.0) x 3,4-Diphenylcyclohex-2-en-lone (500.0 mg, 2013 pmol) added to 14C photolysate (43.88 mg, 176.7 pmol): (lo), 24 mg, 100-102", 0.741-i. 0.015,0.0165 pmol produced, $, = (2.4 &0.3) X 10-5 Control Runs. Run C-1. 4,4-Diphenylcyclohex-2-en-lone -4-14C (171.0 mg, 688.5 pmol) in 40 ml n-dodecane at 75" for 3 hr. The reaction, work-up, and isotope dilution were performed in total darkness. 4,4-Diphenylcyclohex-2-en-lone (505.2 mg, 2034 pmol) added to "C aliquot (10.26 mg, 41.30 pmol): (3), 193 mg, 94-95', 4554 f 23,695.0 pmol recovered. trar1s-5,6-Diphenylbicyclo[3.1.0]hexan-2-one (504.5 mg, 2031 pmol) added to 14C photolysate (20.52 mg, 82.63 pmol): (7), 127 mg, 75-76', no product formed. cis-5,6-Diphenylbicyclo[3.1.0]hexan-2-one (502.3 mg, 2022 pmol) added to 14C aliquot (68.40 mg, 275.4 pmol): (12), 43 mg, 113-114", no product formed. 3,4-Diphenylcyclohex-2-en-lone was not analyzed for in this particular run, since other thermal runs showed no evidence that this product was formed. Run C-2. In this run and run C-3 the minor conversions were found due to room fluorescent light. t~rr~~s-5,6-Diphenylbicyclo[3.l.0]hexan-2-0ne-5-~~C (87.9 mg, 354.0 pmol) in 40 ml of t-butyl alcohol at 69" for 25 hr; activity 12.27 pCi/mmol. rra~~s-5,6-Diphenylbicyclo[3.1.0]hexan-2-one (498.2 mg, 2006 pmol) added to 14C aliquot (10.55 mg, 42.48 pmol): (6), 73 mg, 75-76', 262.8 + 1.4, 366.0 pmol recovered; 0% conversion. 4,4-Diphenylcyclohex-2-en-lone (514.0 mg, 2070 pmol) added to 14C aliquot (35.16 mg, 141.6 pmol): (7), 103 mg, 94-95", 0.036 f 0.016,l.j X 10-2pmol produced, 0 % conversion. cis-5,6-Diphenylbicyclo[3.1.0]hexan-2-one (505.7 mg, 2036 pmol) added to 14Caliquot(5.27 mg, 21.22pmol): (ll), 123 mg, 113-114", 0.021 + 0.007, 5.8 X 3,4-Diphenylcyclohex-2-en-lone (499.3 mg, 201 1 pmol) added to 14C aliquot (36.92 mg, 148.7 pmol): (7), 51 mg, 101-102", 0.025 i 0.003,l X Run C-3. cis-5,6-Diphenylbicyclo[3.1 .O]hexan-2-0ne-5-'~C (78.4 mg, 316.0 pmol) in 40 ml of t-butyl alcohol at 69" for 5 hr; activity 11.97 pCi/mmol. cis-5,6-Diphenylbicyclo[3.1 .O]hexan-2-one (475.4 mg, 1914 pmol) added to 14C aliquot (4.70 mg, 18.92 pmol): (6), 308 mg, 113-114", 119.78 f 0.65, 322.0pmol recovered, 0% conversion. 4,4-Diphenylcyclohex-2-en-lone (480.1 mg, 1933 pmol) added to 14C aliquot (9.41 mg, 37.89 pmol): (5), 200 mg, 94-95", no product formed. trar1s-5,6-Diphenylbicyclo[3.1.0]hexan-2-one (498.0 mg, 2005 pmol) added to 14C aliquot (32.93 mg, 132.6 pmol): (6), 121 mg, 75-76", 0.050 f 0.020,2 X 10-2 pmol produced, 0 % conversion. 3,4-Diphenylcyclohex-2-en-lone (483.4 mg, 1946 pmol) added to 14C aliquot (31.36 mg, 126.3 pmol): (7), 53 mg, 101-102", 0.064 & 0.010, 2.6 X
Studies in organic and physical photochemistry - an interdisciplinary approach
Organic & biomolecular chemistry, 2016
Traditionally, organic photochemistry when applied to synthesis strongly interacts with physical chemistry. The aim of this review is to illustrate this very fruitful interdisciplinary approach and cooperation. A profound understanding of the photochemical reactivity and reaction mechanisms is particularly helpful for optimization and application of these reactions. Some typical reactions and particular aspects are reported such as the Norrish-Type II reaction and the Yang cyclization and related transformations, the [2 + 2] photocycloadditions, particularly the Paternò-Büchi reaction, photochemical electron transfer induced transformations, different kinds of catalytic reactions such as photoredox catalysis for organic synthesis and photooxygenation are discussed. Particular aspects such as the structure and reactivity of aryl cations, photochemical reactions in the crystalline state, chiral memory, different mechanisms of hydrogen transfer in photochemical reactions or fundamental...