The environmental impact of the extensive use of fossil fuels to produce fuels and chemicals as well as the cost sensitivity of platform chemicals to oil prices remain major concerns. Sustainable biomass processing is the only viable solution for the large-scale production of bio-based products with a projected average of 30 % of the production of chemicals to derive from biomass within the EU (Joint European Biorefinery Vision for 2030). The co-production of fuels and high-value bio-derived chemicals would contribute to the environmental sustainability, as well as the economic viability, of the future biorefineries. Lignocellulosic biomass is relatively inexpensive and abundant, without competing with food sources, and thus it can be considered as the most suitable feedstock for a full-scale biorefinery. The production of highly functionalized intermediates such as 5-(hydroxymethyl)furfural (5-HMF) and 2,5-dimethylfuran (2,5-DMF) from lignocellulose has been established. The conversion of such platform chemicals into other high-value products remains a challenge. A plethora of published studies focused on the transformations of the functional groups rather than using the furan ring chemistry. The overall project objective was the study of novel reaction protocols to produce heterocyclic and aromatic platform chemicals from established biomass intermediates by using ionic liquids as catalysts or co-catalysts. Thiophene synthesis from bio-derived furanics, such as 2,5-DMF, was studied under acidic conditions, focusing on Lewis acidic ionic liquids that promoted the recyclization of bio-derived 2,5-DMF into its thiophene analogue. Moisture-stable chlorometallate ILs were synthesised and characterised separately to elucidate speciation, acidity and thermal stability prior to being applied towards thiophene synthesis in liquid-liquid biphasic reactions. Lewis acidic chlorozincate(II) ionic liquids were also supported on an inexpensive, high surface area silica support, affording supported ionic liquids (SILPs) that were studied for their surface properties and IL/support interactions. The SILP materials were successfully tested as catalysts for the novel, gas-phase synthesis of 2,5-dimethylthiophene (2,5-DMT) in a pressurised fluidised bed reactor that was constructed in-house. The latter experiments aimed for process control where parameters such as temperature and substrate/H2S ratios were controlled with the overall process economics improving as a thin layer of ionic liquid was used instead of a biphasic system. 2,5-DMF was also investigated as an activated diene in acid-catalysed Diels-Alder reactions in the presence of maleic anhydride towards the synthesis of phthalic anhydride derivatives. The domino reactions for the formation of 3,6-dimethylphthalic anhydride (3,6-DMPA), a potential precursor for polymer synthesis, was studied in binary IL/acid systems of different acidity profiles, indicating the potential towards the direct synthesis of 3,6-DMPA from bio-based furanic compounds.