Photocycloaddition of acetylacetonatoboron derivatives with simple olefins (original) (raw)
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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.
Tetrahedron, 1999
N-Chloro-alkenylpyrrolidinones, an N-chloro-alkenylsuccinimide and N-chloro-alkenyloxazolidinones were prepared as precursors of olefinic cyclic carboxamidyL imidyl and carbamyl radicals constrained to undergo intramolecniar reactions uniquely via their planar or slightly twisted (30-35 °) I-IN state (l,5-transfer of an allylic hydrogen, 5-exo or 6-exo cyclization to give bicyclo[2.2, l]azaheptane and bicyclo[3.2, llazaoctane skeletons respectively), those intramolecular reactions being unacce~ible to the planar EN state. Their photolysis gave products arising uniquely from intermolecular reactions of those nitrogen radicals (addition to an external olefin, hydrogen abstraction from the solvent, allylic hydrogen abstraction). An intramolecular reaction leading to bicyclo[3.3.0]azaoctane derivatives via 5-exo cyclization was observed with an N-chloro-alkenylpyrrolidinune and an Nchloro-alkenyloxazolidinone. In these two cases, both the FIN and the Es states of the cyclic amidyl radical allow orbital overlap for 5-exo cyclization.
Journal of the American Chemical Society, 1971
Mechanistic studies on the photorearrangements of benzobicyclo[2.2.2]octadienone (1) and bicyclo-[2.2.2]octenone (5) are reported. The limiting quantum yields for the singlet reaction of 1 are: &is = 0.50; @nsphthslene = 0.45; ~4,5-benLobie,c~o[l.l.0100ta-2,1-dion.8~0~~ = 0.10. The limiting quantum yields for the acetophenonesensitized reaction are: adis = 0.14; anaphthslene = 0.01 ; ~b e n r o t r i o y e l o [ 3 . 3 . 0 , 0 2~8~~~t e n~3 . 0 n e = 0.12. A deuterium labeling experiment established the 1,2-acyl migration mechanism for the photosensitized rearrangement of 1. Finally, it was shown that the triplet reaction proceeded by a concerted, symmetry-allowed process by comparison with the photoisomerization of lactone 12.
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.
Tetrahedron, 1997
The irradiation of 1,4-dicyanobenzene (DCB) in the presence of 2,3dimethyl-2-butene (DMB) leads to allylation of the aromatic. In the presence of nucleophiles (MeOH, H20, CF3CH2OH) this reaction is substituted by the nucleophile olefin combination-aromatic substitution (NOCAS) process. The quantum yield increases from 0.006 in the absence to a limiting value of ca 0.02 in the presence of the nueleophiles. The reaction involves competing deprotonation and nucleophile addition to the olefin radical cation, followed by coupling of the thus formed radical with DCB-.. Minor processes are hydrogen abstraction from the solvent by the allyl radical, revealed by isolation of the phenylpentanonitrile 3 and coupling of the radical ions before separation, revealed by a small amount of the cyclohexadiene 6.
2002
The rate constants for the quenching of indane-1,2,3-trione (1) and 5-methoxyindane-1,2,3-trione (2) triplets by olefins, in degassed benzene solution, have been measured by laser flash photolysis. The alkenes studied included acyclic, cyclic, isolated and conjugated dienes, and enol ethers. No quenching was observed when irradiation was performed in the presence of olefins substituted with electron-accepting groups such as maleic anhydride, dimethyl fumarate, dimethyl maleate or chalcone. The plots of log kq versus the ionization potential for cyclohexene, 2-methylbut-1-ene, 2-methylbut-2-ene, 2,3-dimethylbut-2-ene, trans-penta-1,3-diene, ethyl vinyl ether and ethyl prop-1-en-1-yl ether are linear with a slope of -2.7/eV (r = 0.98) for 1 and -2.6/eV (r = 0.95) for 2. The magnitude of the slope is in agreement with a mechanism involving a partial charge transfer complex, which then leads to product formation. A comparison of the reactivity of 1 and 2 toward olefins shows that a similar mechanism operates for the quenching processes of these two triketones.
The photochemical reaction between 1-naphthalenecarbonitrile and some arylalkenes
Journal of Photochemistry and Photobiology A: Chemistry, 1991
Irradiation of I-naphthalenecarbonitrile (NN) and l-phenylcyclohexene (la), l-phenylcyclopentene (lb) or styrene (lc) or in apolar solvents leads to the formation of regioisomeric endo cyclobutane adducts and azabutadienes, resulting from the rearrangement of azetines formed in the primary step. In methanol and methanol-acetonitrile, both P-methoxyethylbenzenes and 1:l:l NN-alkene-methanol adducts (mixture of isomers) are formed. All of these processes occur with quantum yields of 0.05 or less. The effect of donor and methanol concentration, and of the addition of salts and 1,3-cyclohexadiene (no "triplex" Diels-Alder reaction), are used to investigate the mechanism. The main intermediate is a polar exciplex, or radical ion pair, the main fate of which is decay by back electron transfer.
The Journal of Organic Chemistry, 1992
The 3-oxa-1,5-hexadienones 4a, 4b, 5a, and 5b undergo intramolecular [ 2 + 21 photocycloaddition reactions with quantum yields ranging from 0.2 to 0.002. In general, oxa substitution decreases the quantum yields and favors the formation of crossed cloeure producta in comparison to the alkenyl analogs. Irradiation of stereoe~ically deuterated dienones lla and 12a indicate that the intermediate biradical reverts to the starting dienone faster than it proceeds to product. The results are compared with the analogous alkenyl systems. An explanation for changes in regiochemistry, quantum yields, and reversion rates between the two systems is offered.
Photochemical cycloadditions via exciplexes, excited complexes, and radical ions
Accounts of Chemical Research, 1982
Cycloadditions are among the earliest known reactions in organic photochemistry. Some of the classical examples are the 2 + 2 cyclodimerization of olefins such as coumarin,' cinnamic acid,2 and a~enaphthalene;~ the 4 + 4 cyclodimerization of anthracene: PaternbBuchi's oxetane formation5 by 2 + 2 cycloaddition of carbonyl compounds to alkenes; Schonberg's dihydrodioxin for-mation6 by 4 + 2 cycloaddition of o-quinones to alkenes; and Schenck's epidioxide formation7 by 2 + 4 cycloaddition in the photosensitized oxygenation of dienes. Interest in photocycloadditions intensified in the 1960s, when it was discovered that many dimerizations and mixed additions could also be induced by triplet sensitization.s A vast number of cyclobutane derivatives became accessible through these reactions. Besides their synthetic value, these reactions constitute the basis for the technically important photo-crosslinking of polymer^.^ Extensive research on the photophysics of complex formation and electron-transfer processes in the excited state stimulated many investigations of the potential role of such intermediates in photochemical cycloadditions. Indeed, many singlet-excited-state cyclodimerizations were found to proceed via excimers.1° These studies led also to the discovery of several novel reactions and many mechanisms involved in cycloadditions. Some of the features of these reactions are the subject of this Account. Before we discuss these reactions, however, we want to emphasize a few points about the nature of complexes in the excited state and the closely related phenomenon of electron transfer. Excimers, which are dimeric complexes stable only in the excited state, were first discovered by Forster" in pyrene and other aromatic hydrocarbons. They can best be identified by their fluorescence, which is structureless and shifted to longer wavelength from the monomer fluorescence. This shift results from the stabilization energy of the excimer and a repulsion energy at the corresponding ground-state configuration.12 It is generally accepted that excimers have sandwich geometry. Both exciton resonance (*AA-AA*) and Susan L. Mattes (nee Emeis in Davenport, I A) received a B.A. in chemistry from Middlebury College (VT) in 1971 and an M.S. in organic chemistry from Iowa State University, Ames, in 1974. Then she spent 17 months in the Fine Chemicals Division of the Upjohn Co. in Kalamazoo, MI, and 8 months in the Department of Chemistry, University of Wisconsin, Madison, before pining Kodak in 1976. Her current research interests are in the area of organic photochemistry involving exciplex intermedlates and eiectrontransfer reactions. Samir FarM was born in Fayoum. Egypt. He received his B.Sc. and MSc. degrees from Ain-Shams University, Cako. He obtained a Ph.D. from the University of OGttingen (1987) for research conducted at the Max-Planck-lnstiut, Mulheim-Ruhr (G. 0. Schenck). After 2 years as a research assistant at the same institute, he Joined the Kodak Research Laboratories, where he is now a Research Associate. Current research activities include excipiex and electron-transfer reactions, light-sensitive polymers, and photochemistry in polymers and polyelectrolytes. charge-transfer configuration (A' A-A-A') contribute to the excimer state.12 Weller13 discovered that complexes in the excited state are not limited to dimeric species, i.e., excimers, but can also be formed between vastly different molecules. Such complexes were originally termed heteroexcimers and are now referred to as exciplexes. Here, too, the structureless, long-wavelength-shifted emission from exciplexes offers the best means for their investigation. From the solvent dependence of the exciplex fluorescence maximum, the dipole moment of the exciplex and hence the degree of charge transfer within the complex can be e~timated.'~ Temperature-dependence studiesI5 of the exciplex-to-monomer fluorescence ratio revealed that these complexes are formed reversibly, with the forward reaction being mostly diffusion controlled. Association enthalpies and entropies are also obtainable from such temperature-dependence studies.15 Exciplexes with dominant charge-transfer (CT) character are formed, in spite of the lack of ground-state interaction between their components, because molecules become better donors and acceptors in the excited state than they are in the ground state. Excitation in the CT band of an electron-donor-acceptor (EDA) complex gives an excited complex that has stronger binding energy than in the ground state for the same reasons as with exciplexes. Excitation at wavelengths absorbed by only one of the components results in the formation of a complex in the excited state (an exciplex)