Development of methodology for the palladium-catalysed synthesis of oxygen-containing heterocycles

• Main Author: Hewitt, Joanne F. M.
• Published: University of Glasgow 2014
• Subjects: 547; QD Chemistry
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.601592

The opening chapter of this thesis gives an overview of the existing methods to functionalise palladium(II)-alkyl intermediates resulting from oxy- or carbopalladation of unactivated alkenes, outlining the range of heterocycles which can be formed using this type of methodology. A summary of Pd(IV) species in synthesis and catalysis follows, with a focus on Pd(IV) intermediates arising from oxidative addition of alkyl halides to Pd(II) and those suggested in alkene difunctionalisation reactions. As the subsequent formation of sp3–sp3 C–C bonds from Pd(II)-alkyl intermediates was noted as a limitation of prevailing nucleopalladation methods, the second chapter of this thesis outlines the work towards development of an oxypalladation reaction of hydroxyalkenes, with concomitant formation of an sp3–sp3 C–C bond. Allyl halides proved to be competent electrophiles for this transformation. The oxyallylation reaction was successfully applied to a range of hydroxyalkene substrates, with the methodology developed also applied to a 5-step synthesis of anti-depressant citalopram. The oxyallylation reaction constructs heterocycles substituted in the 2-position, forming two new bonds in a single step. Ensuing work, detailed in Chapter 3, focused on the development of an analogous carboallylation reaction, using aryl boronic acid derivatives. This transformation gives rise to the formation of two new C–C bonds in a single step, including the construction of a fully substituted carbon centre. Experimental procedures and data are summarised in Chapter 4.