Studies on asymmetric photoreactions in zeolites
Description
The subject matter of this dissertation examines the possibility of performing stereoselective photoreactions within the constrained reaction cavities of zeolites. This concept was evaluated by carrying out well known photochemical reactions within these zeolites Chapter 1 presents an introduction to the type of asymmetric photoreactions that have been carried out in isotropic and organized media. This chapter also presents the properties of zeolites that make them suitable hosts to carry out stereoselective photoreactions In Chapter 2, the results of five tropolone ethers are presented. Tropolone ethers undergo a 4-pi electrocyclization reaction resulting in chiral bicyclo[3.2.0] products. The photochemistry of the substrates in this chapter was examined in zeolites like NaY modified with chiral organic molecules. The asymmetric environment of the zeolite induces chirallity in the product. These substrates gave an insight into the factors responsible for chiral induction in zeolites Chapter 3 discusses the diastereoselective photoreaction of a chiral tropolone ether. Faujasite zeolites like NaY were used for this reaction. Irradiation in these zeolites gave a significant diastereoselectivity. Upon carrying out the reaction in chirally modified zeolites, a remarkable enhancement of the diastereoselectivity was observed Chapter 4 discussed the synthesis and preliminary photochemical studies of some achiral tropolone derivatives. These substrates could not be investigated in detail due to complications in the photochemistry or the synthesis In Chapter 5, the asymmetric photochemistry of some adamantyl aryl ketones within zeolites is described. These ketones undergo the Norrish type II reaction resulting in cyclobutanol products. When the reactions are carried out in chirally modified zeolites, chiral induction in the cyclobutanol products were observed. The results of two non-chiral substrates and one chiral adamantyl ketone are presented Chapter 6 discusses the di-pi-methane rearrangement of benzonorbornadiene within chirally modified zeolites. The reaction was examined in NaY using a triplet sensitizer. It was also studied in TlY wherein the heavy cation effect affords the triplet product