Hayes, Theodore; (2018) A Novel Enediyne Synthesis from Alkynyl Sulfonamides via Non-Classical Carbenoids. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

In the last forty years Z-enediynes have been found to facilitate a unique and powerful class of antitumour agent, which has already shown some clinical application, and possesses great potential for further use. Meanwhile, an area of continued research interest within the Wilden group has been exploration of the chemistry of alkynyl sulfonamides, which remains relatively unreported to date. Furthermore, within the literature there has been a growing concern to find alternative synthetic routes that obviate the necessity of transition metal catalysts, given their often high toxicity, expense and difficulty of removal from final products. In this thesis, an original synthesis of Z-enediynes upon treatment of alkynyl sulfonamides with lithiated acetylene derivatives is described, without the use of transition metals. Alongside this, alkenyl sulfonamide and 1,3-diyne side-products were usually observed, the latter of which has various useful applications itself. Extensive investigations involving classical experimentation and computational modelling revealed a fascinating collection of mechanistic routes, significantly differing from other alkynyl sulfonamide reactions performed within the group. It was subsequently discovered, that an unusual non-classical carbenoid intermediate is responsible for the formation of the Z-enediyne and alkenyl sulfonamide products. Meanwhile, a conventional addition-elimination pathway produces the 1,3-diyne. The proportions of the three products can be regulated to a degree by altering the synthetic parameters, however these effects are limited. Determination of the optimum conditions for each product was attempted using DoE experiments, although these were relatively unsuccessful. Work was also done to incorporate the novel Z-enediyne synthesis into the existing preparations of enediyne antitumour agents, but was hindered by polymerisation side-reactions. Finally, the scope of suitable starting material substrates was explored, which yielded curious changes to the reaction’s progression. Possible explanations are provided for these observations, contributing further to the continued research of alkynyl sulfonamide chemistry.

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