da Mata, Maria Lucília E. N.; (1994) Intramolecular radical aromatic substitution reactions. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis is divided into three chapters. Chapter One presents a review on ipso substitution in aromatic and heteroaromatic rings, and is divided in two parts. The first is concerned with intermolecular ipso substitution reactions and the second describes the work that has been done on the intramolecular reactions. Chapter Two describes the advances of an intramolecular free radical ipso substitution strategy which uses a sulfonyl moiety as an ipso nucleofuge. The reaction of an aryl radical with a sulfonyl substituted acceptor ring, with differing substituents on the acceptor ring and tethering chains of different nature and size, is discussed. A strong effect on the promotion of ipso substitution was found with compounds where an ortho substituent to the sulfonyl substituted position was present. In the absence of an ortho substituent, preferential attack occurs in order to give the more stable radical. The nature of the bridge between the two aromatic rings is also an important factor, and a slight change in the strain or conformation can change the course of the reaction. With simple chains was observed that in 1,5-ipso substitution reactions, a nitrogen atom is a more efficient ipso director than an oxygen atom, which in turn is better than a methylene unit. 1,6-Ipso substitution reactions were shown to be less efficient processes. Several linking chains, resulting from the combination of nitrogen, oxygen, methylene and carbonyl units were analysed, and in general ipso substitution products could be obtained, although, in some cases, only by the strategical introduction of ortho substituents. A preliminary study on 1,5-ipso substitution reactions of a-carbonyl radicals was undertaken, in order to optimise the reaction conditions. Reactions involving tin compounds, transition metals and xanthates were studied. When tin hydride was used, the formation of indolone derivatives, by a sequential 1,5-ipso substitution / 1,5-addition of the intermediate amidyl radical to the aromatic ring was observed. The temperature of the reaction was shown to be an important factor, as other competitive processes, such as reduction or β-scission can also occur. Chapter Three provides a formal account of the experimental results and procedures.

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