Selectivity in photochemical reactions carried out within zeolites
Description
The subject matter of this report explores the utility of zeolite as a reaction medium to carry out select organic photochemical transformations. Product selectivities obtained in these reactions will be used to explain interactions between the zeolite framework and adsorbed guest molecules Chapter I provides a brief introduction to zeolites including aspects like its availability, structural features, utility as a medium, guest location within zeolites, etc. Selectivity obtained in certain thermal and photochemical reactions carried out within zeolites will be discussed Chapter II focuses on 'regioselectivity' evidenced in the photo-Fries and photo-Claisen rearrangement reactions of a series of naphthyl and phenyl esters, and ethers. The selectivity is postulated to be due to interactions between reactive intermediates and cations present in the zeolite framework. Also noticeable within zeolites is an enhanced 'heavy atom effect', resulting in higher intersystem crossing rates for the adsorbed substrates Chapter III deals with the decarbonylation reactions of a series of naphthyl esters and dibenzyl ketones. Decarbonylation of the naphthyl esters, facile in isotropic media, does not occur within zeolites. Dibenzyl ketones, however, show facile decarbonylation rates both in zeolites and isotropic media. Within heavy atom zeolites, rearrangement products predominate over decarbonylation products for dibenzyl ketone. This suggests enhanced intersystem crossing in the biradical intermediates formed during the course of the reaction Chapter IV deals with the decarboxylation reactions of a series of naphthylmethyl esters. These esters tend to form different photoproducts depending on the polarity of the zeolites used Chapter V discusses different strategies to selectively generate the triplet excited states of adsorbed guest molecules within zeolites. Three different techniques, heavy atom effect, light atom effect, and sensitization using known triplet sensitizers will be explored. Merits and demerits, in terms of how effective these techniques are on the different substrates investigated will be discussed in detail