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)
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.
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.
J Am Chem Soc, 1979
Although the photochemical behavior of the carbonyl group has received much scrutiny in the past d e~a d e ,~.~ relatively little is known about the photochemistry of the small amount of enol tautomer which exists in equilibrium with the keto In an earlier reportS dealing with the photorearrangement of 4-phenyl-3-chromanone (1) to 4-phenyldihydrocoumarin (2),6 evidence was presented which demonstrated that the enol content can be an overriding factor in determining the quantum efficiency of a photoreaction. As part of our continuing studies dealing with enol photoc h e r n i~t r y ,~~~ we have undertaken an investigation of the excited state behavior of the 4-carbomethoxy-3-chromanone (3) system. W e now report that in extending our studies to this system, we have discovered an unusual solvent effect which controls the product distribution. In addition, we have uncovered a n unprecedented photodecarbonylation reaction which can best be explained by invoking the intermediacy of a transient cyclopropanone.
Photochemistry of bridged cycloheptadienones
Tetrahedron, 1974
A series of 6,7-Benzobicyclol3.2.l]octadienes (10-13) have been prepared. Direct and sensitized irradiation of the dienes gave di-m-methane rearrangement products (M-17). Quantum yields for the direct and sensitized rearrangements were recorded and compared. Substituent effect and structure-multiplicity relationships are discussed.