Stereoselective photocatalytic reaction

In this chapter, we will discuss what type of chiral photosensitizer is applied to stereoselective photoinduced electron transfer reaction, what type of substrate is used, and what type of chiral functional group is introduced to these compounds to construct a chiral photosensitizer. We will describe also the stereoselective photocatalytic reactions. 

C. Application of Chiral Ruthenium(ll) Complexes to Stereoselective Photocatalytic Reactions... 

Selective synthesis of a target stereoisomer is one of the most important and significant processes. Hence, achievement of stereoselective synthesis by photocatalytic reaction is also strongly desired. There are three possibilities for the stereoselective syntheses by semiconductor photocatalytic reaction in the step of (1) oxidation by a positive hole, (2) included chemical reaclion(s), e.g., condensation into a Schiff base, and/or (3) reduction by an excited electron. An example of (1) is the photocatalytic L-PCA synthesis from Lys the optical purity depends on the position of the amino group which the positive hole attacks. To the... 

Some other catalytic events prompted by rhodium or ruthenium porphyrins are the following 1. Activation and catalytic aldol condensation of ketones with Rh(OEP)C104 under neutral and mild conditions [372], 2. Anti-Markovnikov hydration of olefins with NaBH4 and 02 in THF, a catalytic modification of hydroboration-oxidation of olefins, as exemplified by the one-pot conversion of 1-methylcyclohexene to ( )-2-methylcycIohexanol with 100% regioselectivity and up to 90% stereoselectivity [373]. 3. Photocatalytic liquid-phase dehydrogenation of cyclohexanol in the presence of RhCl(TPP) [374]. 4. Catalysis of the water gas shift reaction in water at 100 °C and 1 atm CO by [RuCO(TPPS4)H20]4 [375]. 5. Oxygen reduction catalyzed by carbon supported iridium chelates [376]. - Certainly these notes can only be hints of what can be expected from new noble metal porphyrin catalysts in the near future. 

Selective encapsulation of substrate(s), preorganization of substrates in the confined space of the NR, and an increase of local concentration within the NR can result in unusual regio- and stereoselectivity, reaction rate, and yield, and an alteration in the reaction pathway. It is worth nothing that NRs can also be used in photochemical reactions and development of photocatalysts. As an example, dendrimer-protected Tt02 nanoparticles were synthesized and their photocatalytic activity was compared to that of Ti02 nanoparticles in photodegradation of 2,4-dichlorophenoxyacetic acid. The results indicated the superior activity of dendritic photocatalysts, which was attributed to stabilization of nanoparticles and reinforcement of photocatalytic activity [43]. 

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