Photochemistry of 7-Alcoxy and Thioalcoxy-3,3-dimethoxybicyclo(2.2.2) oct-5-en-2-one. Sequence 1,3-acyl shift-decarbonylation reaction (original) (raw)
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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.
J Am Chem Soc, 1971
The photolysis in benzene of endo-5-benzoylbicyclo[2.1 .l]hexane (5) has been found to afford A3-cyclopentenylacetophenone (7) and 2-pheny1tricyclo[3.2.0.03~7]heptan-2-ol (8). Tricyclic alcohol 8 was found to rearrange thermally to A3-cyclopentenylacetophenone. In the presence of 90 x acetic acid, tricyclic alcohol 8 rearranged to give 2-phenyl-2-norbornen-exo-6-01 (ll), 2-phenyl-6-exo-acetoxy-2-norbornene (12), 2-phenyltricyclo-[2.2.1 .02 ?6]heptan-3-01 (13), and 2-phenyl-3-acetoxytricyclo[2.2.1 .0*t6]heptane (14). The photochemical transformations encountered in this work appear to be best described by a transannular hydrogen abstraction followed by subsequent reactions of the diradical thus formed. The photoreactions were shown to proceed by way of a triplet n-a* state. In striking contrast to the extraordinarily slow cyclobutylphenyl ketone system, both exo-and endo-5-benzoylbicyclo[2.1 .l]hexanes were found to rearrange at a faster rate than valerophenone. The inefficiency of these reactions (CP exo = 0.06, CP endo = 0.20) can be attributed to an unusually rapid triplet degradation. n the preceding paper, it was shown that the irradia-
Tetrahedron Letters, 1979
The triplet sensitized irradiation of 3-allyl-diaryl-substituted cyclopropenes to m.l.O]hex-2-enes proceeds via an intramolecular [2+2]-cycloaddition followed by a subsequent rearrangement of the initially formed tricycl0[2.2.0.0~~~]hexane skeleton. Previous work from this laboratory has shown that the direct irradiation of 3-allyl-3methyl-1,2-diphenylcyclopropene (1) afforded 1,2-diphenyl-3-methylbicyclo[3.l.O]hex-3-ene (3) as the exclusive photoproduct.' The most reasonable explanation to account for the formation of 2 involves ring opening of the electronically excited singlet state of 1 to a vinylcarbene intermediate (g).2-4 Attack of the carbene carbon on the neighboring double bond generates the bicyclo[3.l.O]hexene skeleton. The photochemical reaction encountered on direct irradiation proceeds through the singlet manifold since irradiation of 1 in the presence of a triplet sensitizer gave rise to the isomeric bicyclohexene i.5
Photochemical Reactions of 1,3,3-Trimethylbicyclo[2.2.2]octa-5,7-dien-2-ones
European Journal of Organic Chemistry, 2006
The photochemistry of 1,3,3-trimethylbicyclo[2.2.2]octa-5,7-dien-2-ones 1a–f containing multiple chromophoric moieties under various conditions is described. Upon direct irradiation, dienones 1a–f in benzene, acetonitrile, and methanol were found to aromatize through photoelimination of dimethylketene, which was trapped with 3-phenylprop-2-en-1-ol (12). Triplet sensitization of dienone 1a in acetone and in acetone/acetophenone mixed solvents afforded aromatic compound 2a, whilst bicyclic systems 1b–c were found to be unreactive on sensitization. In the cases of dienones 1d–f in acetone, aromatic compounds 2d–f and di-π-methane (DPM) photoproducts 3d–f and 4f were observed, but in the acetone/acetophenone mixed solvent system only DPM photoproducts were detected. Plausible mechanisms for these photochemical reactions are described. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
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.
Journal of Photochemistry and Photobiology A: Chemistry, 2000
On irradiation of 4-phenoxybut-1-enes substituted with a carbomethoxy group in the arene, only the ortho compound 1 led to notable ortho photocycloaddition, while the meta regioisomer 2 furnished meta and ortho photocycloadducts albeit in low yield, and the para-substituted compound 3 resulted only in intractable polymers. On irradiation of the carboxymethyl-and 2-carboxyethyl homologues 4-9, the photoreactivity altered dramatically. The highest yields of meta photocycloadducts were observed on irradiation of the ortho-substituted compounds 4 and 7. Due to steric hindrance, only one of the two possible regioisomers 18 and 19, respectively, was formed. The meta-substituted compounds 5 and 8 gave significant amounts of meta photocycloadducts as mixtures of regioisomers 13+16 and 14+17, respectively. The intramolecular meta photocycloaddition was directed exclusively to the 2 ,6-positions of the arene and only 1,5-bridged dihydrosemibullvalenes were formed. On irradiation of the ortho-and para-substituted compounds 4 and 7, and 6 and 9, respectively, considerable amounts of reaction products derived from initial ortho photocycloaddition were detected.
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.