Synthesis of novel symmetrical and unsymmetrical aza BODIPY analogues.

Abstract

This thesis is focused on the expansion of the synthetic study of aza (dibenzo) BODIPY analogues. It describes a more detailed investigation of the formation of the precursor aminoisoindolines using reaction of alkyl and benzyl acetylenes with bromo benzamidine under microwave conditions. Treating the amidine with 1-hexyne under Sonogashira copper-free cross coupling reaction conditions led to unexpected formation of the six-member ring compound, 3-butyl isoquinoline-1-amine was isolated in 31% yield. However, using aryl acetylene in the synthesis of the precursor aminoisoindolines successfully produced the required 5-member ring compounds (aminoisoindolines) in good yield. Therefore, a variety of new symmetrical and unsymmetrical aza BODIPYs and their precursors aza (dibenzo) dipyrromethenes bearing electron withdrawing or electron donating substituents have been smoothly synthesised and isolated in good yield. Initially the synthesis of unsymmetrical analogues was achieved using simple mixed condensation reactions. Approximately statistical mixtures were produced when the precursor aminoisoindolenes were electronically similar. However, when they were different, the reaction favoured the formation of the two symmetrical derivatives. Consequently, a new synthetic procedure has been developed to control the synthesis of unsymmetrical analogues by converting of the amino group of one aminoisoindoline into good leaving groups such as triflate or tosylate. This successfully led to favour formation of the unsymmetrical aza (dibenzo) dipyrromethenes with reaction yields of up to double those obtained via the mixed condensation synthetic method (50% - 64%). Complexation of symmetrical and unsymmetrical aza (dibenzo) dipyrromethenes with BF3.OEt2 was successfully optimized by treating the mixture with TMS-Cl to remove the fluoride ion which led to shift the equilibrium towards the target aza BODIPYs with remarkable improvement in the outcome. The final part of the thesis describes attempts to cyclise aza dipyrromethenes to form porphyrin-like macrocycles. Unfortunately, these attempts were unsuccessful due to a combination of low reactivity and isomerisation of the precursors in the presence of any metal.