• Journal of Photoscience
• /
• v.7 no.1
• /
• pp.5-8
• /
• 2000

Irradiation of 2'-bromobenzanilide in acetonitrile containing sodium hydroxide under nitrogen leads to the formation of the intramolecular photosubstituted product, 2-phenylbenzoxazole (45 %) along the minor photoreduced and photo-Fries type product. The photoreaction of 2'chlorobenzanilide under the same condition as above gives the photo-Fries type reaction product, 2-amino-3-chlorobenzophenone (22%) with minor product, 2-phenylbenzoxazole. The photoreaction of 2'-chlorobenzanilide in acetonitrile produces a photocyclized product, phenanthridone (19%) along with minor products, 2-phenylbenzoxazole, benzanilide, 2-amino-3-chlorobenzophenone, and 4-amino-3-chlorobenzophenone, while that of 2'-bromobenzanilide produces photosubstituted product, 2- phenylbenzoxazole.

• Journal of Photoscience
• /
• v.3 no.2
• /
• pp.61-64
• /
• 1996

Photoaddition reactions of p-quinones to 1, 4-diphenylbubl-en-3-yne (BEY) have been investigated. Irradiation (300 nm) of BEY and 1, 4-benzoquinones in dichloromethane afforded quinone methides. I rradiation of 1, 4-naphthoquinone and BEY leaded to the formation of unstable spiro oxetene intermediate, followed by the rearrangement to give quinone methide, and finally the oxidative photocyclization. In contrast, irradiation 2, 3-dichloro-1, 4-naphthoquinone (or anthraquinone) and BEY yielded another type of quinone methides in one pot.

• Bulletin of the Korean Chemical Society
• /
• v.34 no.12
• /
• pp.3681-3689
• /
• 2013

This study explored a direct SET-photochemical strategy to construct a new family of thioene conjugated-naphthalamide fluorophore based lariat-crown ethers which show strong binding properties towards heavy metal ions. Irradiations of designed nitrogen branched (trimethylsilyl)methylthio-terminated polyethylenoxy-tethered naphthalimides in acidic methanol solutions have led to highly efficient photocyclization reactions to generate naphthalamide based lariat type thiadiazacrown ethers directly in chemo- and regio-selective manners which undergo very facile secondary dehydration reactions during separation processes to produce their corresponding amidoenethio ether cyclic products tethered with electron donating diethyleneoxy- and diethyenethio-side arm chains. Fluorescence and metal cation binding properties of the lariat type enamidothio products were examined. The photocyclized amidoenethio products, thioene conjugated naphthalamide fluorophore containing lariat-thiadiazacrowns exhibited strong fluorescence emissions in region of 330-450 nm along with intramolecular exciplex emissions in region of 450-560 nm with their maxima at 508 nm. Divalent cation $Hg^{2+}$ and $Pb^{2+}$ showed strong binding to sulfur atom(s) in side arm chain and atoms in enethiadiazacrown ether rings which led to significant enhancement of fluorescence from its chromophore singlet excited state and concomitant quenching of exciplex emission. The dual fluorescence emission responses towards divalent cations might provide a new guide for design and development of fluorescence sensors for detecting those metals.

• Journal of Photoscience
• /
• v.10 no.1
• /
• pp.89-96
• /
• 2003

Two important types of $\alpha$-heterolytic fragmentation reactions of aminium radicals are discussed. In these fragmentation processes, transfer of electrofugal groups from the aminium radicals to either Lowry-Bronsted or Lewis bases produces $\alpha$-amino radicals. The results of recent studies that provided key information about the dynamics of the important aminium radical fragmentation reactions, deprotonation, desilylation, are summarized. Finally, selected examples, which demonstrate how knowledge of the relative rates of aminium radical cleavage can be used to design synthetically relevant SET-promoted photocyclization reactions, are presented.

• Bulletin of the Korean Chemical Society
• /
• v.29 no.1
• /
• pp.89-93
• /
• 2008

The key step in a strategy for the synthesis of (+)-lactacystin involving photocyclization reaction of a cyclopenta-fused pyridinium salt has been probed by using a model substrate. Observations made in this effort led to the discovery of a highly unusual cascade process that leads to stereoselective formation of an interesting tricyclic carbamate. The results of this study are presented and discussed in the context of a (+)-lactacystin synthetic approach.

• Bulletin of the Korean Chemical Society
• /
• v.27 no.8
• /
• pp.1099-1114
• /
• 2006

Our studies in the area of single electron transfer (SET) photochemistry have led to the discovery of efficient processes, in which regioselective formation of carbon-centered radicals takes place by nucleophile assisted desilylation of $\alpha$-trialkylsilyl substituted ether, thioether, amine and amide centered cation radicals. The rates of bimolecular desilylation of the intermediate cation radicals exceed those of other cation radical $\alpha$-fragmentation processes (e.g.,-deprotonation). This sereves as the basis for the design of highly regioselective, SET-induced photomacrocyclization reactions of polyether, polythioether, polyamide, and polypeptide linked phthalimides. Photocyclization reactions of trimethylsilyl-terminated substrates in these families are unique in that they produce polyfunctionalized macrocyclic substances in a highly efficient and regioselective manner. In addition, our studies in this area have led to important information about the factors that govern chemical and quantum efficiencies that should be applicable to a wide variety of redox processes promoted by SET from substrates containing more than one electron donor site.

• Journal of Photoscience
• /
• v.4 no.1
• /
• pp.7-10
• /
• 1997

The structures of 8-membered azalactone isomers produced from photocyclization of 2-(N,N-dibenzylamino)ethyl benzoylacetate were determined by the X-ray structure analysis to clarify the stereochemical behavior of a 1,8-biradical. The remarkable stereoselectivity in cyclization of the 1,8-biradical to form cis- and trans-isomers of the azalactone was not observed. The ring conformations were boat-chair like and dihedral angles between C$_5$- and C$_6$- phenyl groups were ca 45$\circ$ in the both isomers. The 1,8-biradicals in the transition state for the cyclization would have nearly same boat-chair like conformation and twisted configuration with the dihedral angle of ca 45$\circ$ as the corresponding isomer, and this is responsible for luck of stereoselectivity in long-chain biradical cyclization.

• Bulletin of the Korean Chemical Society
• /
• v.6 no.4
• /
• pp.234-238
• /
• 1985

The photoisomerization of 5-styryl-1,3-dimethyluracil is studied with nanosecond laser flash photolysis technique at room temperature. The laser flash photolysis of E-isomer produces the transient absorption spectrum regarded as the triplet-triplet absorption, but the transient absorption of Z-isomer does not show the typical decay curve, probably due to the facile photocyclization reaction during the laser flash photolysis. Using the energy transfer method on nanosecond laser spectroscopy, the energy of the lowest triplet state for E isomer is estimated to lie between 41.8 and 47 kcal/mol. The triplet lifetime for E-isomer obtained from the decay curve of the transient absorption is ca. 93ns. The $S_1 → T_1$ intersystem crossing of E-isomer on direct excitation is relatively inefficient at room temperature supporting the singlet mechanism for direct photoisomerization.