The use of tri-n-butyltin hydride and an initiator to mediate free radical cyclisation as a
synthetic organic process is well documented throughout the chemical literature. By using
BU3SnH, and developing new 'catalytic' BU3SnH methods, many new heterocyclic
compounds have been synthesised successfully. The search for new 'tin-free' radical reagents
is important in order to provide a non-toxic alternative to tin. We have started initial studies
on the replacement oftriorganotin hydrides with germanium analogues. An interesting
number of reactions using BU3SnH do not give reduced products and have an oxidation step
in the mechanism. These BU3SnH mediated cyclisations provide a useful synthetic method.
Our studies were aimed at developing the synthetic protocol as well as determining the
'Shilajit' is an ancient tribal panacea, believed to have many advantageous biological
properties. The active constituents are based upon a benzochromenone skeleton. The key
component of the natural product Shilajit, 3-methoxy-6H-benzo[c]chromen-6-one, as well as
several analogues have been synthesised using this BU3SnH mediated 'oxidative' free radical
approach. The mechanism proposed for these reactions by Bowman et ai, the pseudo SRN I
mechanism, has also been studied in order to try to determine the presence of the radical
anion intermediates which are essential for the pseudo SRN 1 mechanism to be correct.
The BU3SnH mediated 'oxidative' cyclisation protocol was successfully applied to electron
deficient pyrroles, i.e. pyrroles with electron withdrawing substituents. Radicals generated
on N-substituted chains readily undergo cyclisation onto the pyrrole ring. The protocol was
also applied to cyclisation reactions of analogous imidazoles. The imidazole reactions were
used for an extensive examination of the mechanism of the 'oxidative' BU3SnH protocol. The
studies have disproved the pseudo SRN 1 mechanism (where BU3SnH is the oxidising agent)
and suggest possible alternative oxidising agents. The importance of the functionality on the
heterocyclic ring is also emphasised. Free radicals have been generated using photolytic
methods, and the results are contrasted with those from traditional BU3SnH reactions. The
synthesis of several substituted pyrazoles and radical cyclisation reactions were attempted on
various pyrazole systems with the aim of synthesising the natural product withasomnine.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.