Controlling photochemical reactions through well structured hosts (cyclodextrins and diol hosts)
Description
This thesis examines the concept that well structured hosts provide an ideal environment for carrying out selective (stereo and regio) photochemical reactions. Three naturally occurring cyclodextrins and one achiral diol host has been used for the study. Using prochiral, chiral and achiral organic molecules as probes the usefulness of this concept was explored Chapter one provides an introduction to the two hosts. It presents properties of the hosts studied and reasoning for why they were considered. Since four photochemical systems have been studied in cyclodextrins and two in the diol host, a detailed introduction has been provided for cyclodextrins followed by a more general introduction for the diol host Chapter two discusses the results of tropolone ethers studied within cyclodextrins. Tropolone ethers undergo a 4-pi electrocyclization resulting in chiral products. Using the inherently chiral cyclodextrin as a host for this reaction, the stereo-chemical outcome of the products formed was examined Chapter three discusses the photoisomerization of diphenyl cyclopropanes and its derivatives inside cyclodextrins. The probes provide insight into how the process of chiral control may be occurring inside the host and help understand how the rigidity of the host can control the stereoselectivity of guests. It also points out the importance of moisture in carrying out these photoisomerizations inside cyclodextrins Chapter four discusses the photocyclization of cyclohexadienones and naphthalenone systems in cyclodextrins. The host did not provide a very suitable environment for the photochemical reaction. Conversions were very low. It did, however, provide insights into the polarity of the host Chapter five examines the regioselective capacity of cyclodextrins. Photo-Fries rearrangement reactions of naphthyl phenyl esters were investigated. The primary aim of this project was to see how much regio control the cyclodextrin interior has to offer Chapter six examines the possibility of a crystalline achiral host controlling the stereochemical outcome of a photoreaction. Though the result obtained using a chiral tropolone was very successful, the host did not work with other chiral guests studied