**8. C-C bond formation**

The C-C bond formation between an electrophilic alkene and adamantane was achieved by the irradiation of TiO2 suspensions in the presence of isopropylydenmalonitrile (IPMN, 0.02 M, with adamantane likewise 0.02 M) and under nitrogen forms a new product as an adduct, 2-[1-(1-adamantyl)-1-methyl)]ethylpropanedicarbonitrile (35% yield), together with traces of oxygenated products, such as 1-adamantanol, 2-adamantanol and 2-adamantanone [66]. By adding silver sulfate as a sacrificial electron acceptor, the yield increased to 75%. The singleelectron transfer oxidation of adamantane is followed by deprotonation leading to the 1 adamantyl radical that couples with isopropylydenmalonitrile.

## **9. Cyclization reaction**

Intramolecular cyclization of N-(β-hydroxypropyl)-ethylenediamine in the presence of a semiconductor (TiO2 or CdS or ZnO)-zeolite composite catalysts in O2 atmosphere produces 2-methylpiperazine and piperazine [67]. The yield of 2-methylpiperazine and piperazine depends on the type of semiconductor and zeolite. Zeolites modified with TiO2 (5 wt% TiO2– Hβ) composite considerably facilitated the intramolecular cyclization with a yield of 31.9%. Zeolites modified with semiconductors ZnO and CdS showed lower activity. This is due to moderate hydrophobicity and acid site strength offered by TiO2-zeolite composite for the cyclization reaction. Selvam and Swaminathan have shown one-pot synthesis of quinaldines from nitroarenes by combined redox-cyclization reaction assisted by photocatalytic method using pure TiO2 and Au-loaded TiO2 catalyst in absolute ethanolic solution under UV radiation (*λ* = 365 nm) [68]. The Au-loaded TiO2 catalyst exhibited higher efficiency and selectivity for the formation of quinaldine and substituted quinaldine from nitrobenzene and substituted nitrobenzene. For instance, TiO2 produced 60% yield and Au/TiO2 produced 75% yield. The reaction involves two steps: in the first step nitro group is reduced to amine, which is followed by condensation with aldehyde and cyclization occurs. The substituted nitrobenzene influen‐ ces the activity and selectivity. The authors suggested that the electron-releasing group at paraposition inhibits the condensation of amino group with aldehyde. 4-Methoxynitrobenzene has a strong electron-releasing group at para-position and showed lower quinaldine yield (60%). Steric effect also plays an important role in product formation. In 3,5-dimethylnitrobenzene and 3-nitrotolune, the cyclization reaction is hindered due to steric effect in 3,5-dimethylni‐ trobenzene and decreased the product yield (70%) when compared to 3-nitrotolune (80%).

## **10. Conclusions**

visible light-driven for photo-oxidation of various PAHs in acetonitrile in O2 atmosphere. Compared to pure BiVO4, Ag-loaded BiVO4 photocatalyst remarkably improves adsorptive and photo-oxidative performance on the degradation. Anthraquinone is obtained in both pure and Ag-loaded BiVO4 solutions, while the amount of formation using Ag-BiVO4 is much larger than that using pure BiVO4. Anthrone is obtained only from the irradiated Ag-BiVO4 solution but not from the pure BiVO4 one. The amount of anthraquinone formation is largest in O2 saturated solution compared to that in N2 atmosphere. Bz[a]A was degraded by Ag-BiVO4 and converted into a considerable amount of 7,12-dione. Substituent effects on the photocatalytic oxidation of naphthalene demonstrate that in dinitronaphthalene isomers, namely 1,3 dinitronaphthalene (1,3-diNN), 1,5-dinitronaphthalene (1,5-diNN) and 1,8-dinitronaphtha‐ lene (1,8-diNN), the photocatalytic oxidation rates followed in the order 1,3-diNN > 1,8-diNN

The C-C bond formation between an electrophilic alkene and adamantane was achieved by the irradiation of TiO2 suspensions in the presence of isopropylydenmalonitrile (IPMN, 0.02 M, with adamantane likewise 0.02 M) and under nitrogen forms a new product as an adduct, 2-[1-(1-adamantyl)-1-methyl)]ethylpropanedicarbonitrile (35% yield), together with traces of oxygenated products, such as 1-adamantanol, 2-adamantanol and 2-adamantanone [66]. By adding silver sulfate as a sacrificial electron acceptor, the yield increased to 75%. The singleelectron transfer oxidation of adamantane is followed by deprotonation leading to the 1-

Intramolecular cyclization of N-(β-hydroxypropyl)-ethylenediamine in the presence of a semiconductor (TiO2 or CdS or ZnO)-zeolite composite catalysts in O2 atmosphere produces 2-methylpiperazine and piperazine [67]. The yield of 2-methylpiperazine and piperazine depends on the type of semiconductor and zeolite. Zeolites modified with TiO2 (5 wt% TiO2– Hβ) composite considerably facilitated the intramolecular cyclization with a yield of 31.9%. Zeolites modified with semiconductors ZnO and CdS showed lower activity. This is due to moderate hydrophobicity and acid site strength offered by TiO2-zeolite composite for the cyclization reaction. Selvam and Swaminathan have shown one-pot synthesis of quinaldines from nitroarenes by combined redox-cyclization reaction assisted by photocatalytic method using pure TiO2 and Au-loaded TiO2 catalyst in absolute ethanolic solution under UV radiation (*λ* = 365 nm) [68]. The Au-loaded TiO2 catalyst exhibited higher efficiency and selectivity for the formation of quinaldine and substituted quinaldine from nitrobenzene and substituted nitrobenzene. For instance, TiO2 produced 60% yield and Au/TiO2 produced 75% yield. The reaction involves two steps: in the first step nitro group is reduced to amine, which is followed by condensation with aldehyde and cyclization occurs. The substituted nitrobenzene influen‐

adamantyl radical that couples with isopropylydenmalonitrile.

> 1,5-diNN [65].

**8. C-C bond formation**

156 Applied Photosynthesis - New Progress

**9. Cyclization reaction**

There is an extensive research and dramatic growth going on in the field of heterogeneous photocatalysis. This method has been commercialized in various aspects of environmental detoxification. Photocatalysis method can be successfully applied for fine organic chemical synthesis. The advantages of photocatalysis method in organic synthesis include the possibility of utilizing clean and abundant renewable energy source, harmless chemicals used as catalysts, reaction can be carried out at room temperature, product type and its selectivity can be tuned by varying the nature of solvent, atmospheric condition, and wavelength of light source used, catalyst reusability, etc. Various challenging aspects have to be considered before implement‐ ing in industrial scale. Most commonly, simulated sunlight or UV sources are used in the laboratory. Experiments need to be devised to monitor the performance of the catalyst in sunlight. In future, more catalysts need to be devised that can trap the visible radiations as well. Since organic solvents are utilized in organic transformations, the band gap of the metal oxide photocatalysts in organic medium has to be explored. Systematic study has to be conducted to optimize the reaction parameters and understand the reaction mechanism, thereby the product yield could be improved.
