Biomass pyrolysis is a promising technology for the production of renewable fuels, due to fast conversion rates, simplicity of operation, and feedstock flexibility. However, the decrease of crude oil prices due to the overproduction makes biofuel economically unattractive, which motivates the formation of a wider product portfolio (especially the production of valuable chemicals) than only fuels for biomass pyrolysis. Anhydrosugars are valuable chemicals primarily prepared from biomass-derived carbohydrate pyrolysis. These molecules are highly desirable precursors used in the synthesis of drugs, surfactants, polymers, and others. However, anhydrosugars are difficult to synthesize in large quantities with high selectivity and yield due to various competing pathways during pyrolysis, making this approach economically unfeasible. A lack of understanding of the fundamental pyrolysis chemistry hinders the development of this field. A simple, cheap, and reliable method to produce anhydrosugars with high selectivity and yield would be a game-changing breakthrough in biomass pyrolysis field. In this work, we developed a two-step ex-situ “ring-locking” strategy to alter the nonselective condense-phase chemistry of carbohydrate pyrolysis. In this method, an alkoxy or phenoxy substitution was introduced at the anomeric carbon of glucose prior to thermal treatment. Through this ring-locking step, we found that the selectivity to 1,6- anhydro-β-D-glucopyranose (levoglucosan, LGA) increased from 2% to greater than 90%. DFT analysis indicated that LGA formation becomes the dominant reaction pathway when the substituent group inhibits the pyranose ring from opening and fragmenting into non-anhydrosugar products. To ease scale-up issues, we further developed a one-step in-situ “ring-locking” method for LGA production. We demonstrated that co-mixing an alkali/alkaline earth salt (e.g., Na2SO4) with an acid (e.g., H2SO4) selectively passivated the sugar ring and significantly enhanced the yield of LGA from 6% to as high as 40% during glucose pyrolysis. Compared with other Group I and Group II metal salts, the co-addition of Na2SO4 was found to give the best LGA yield due to the moderate electronegativity of sodium cation, which led to the preferred binding at ring oxygen site and hindered H+ initiated ring-opening reactions. Additionally, sulfate anions were found to protect LGA from further reactions likely through the complexation with the hydroxyl oxygen of glucose. As an extension of the in-situ “ring-locking” method, I provided a general approach to mediate the condense-phase chemistry by co-mixing the metal salt with glucose. We found that the product spectrum (primarily the yields of LGA and LGO) can be tuned by adding Fe2(SO4)3 at different loadings. The co-addition of Na2SO4 with Fe2(SO4)3 can selectively stabilize the sugar ring and enhance the yields of LGA and LGO, likely through the competition between Na+ and Fe3+ for the oxygen sites. These works first introduced the ring-locking concept to alter the non-selective chemistry of sugar pyrolysis and suggest an economical and simple thermo-chemical approach for upgrading simple and complex carbohydrates. To scale-up our lab discovery into a prototype, we studied the interplay between reaction kinetics and heat and mass transport phenomena during fast pyrolysis. Through characteristic times analysis, we categorized the operating conditions (particle size and temperature) into different regimes based on the dominant phenomenon, and identified mass transfer is the key descriptor for LGA yields. Furthermore, we explored the commercialization potential of our LGA product. We received $50K grant from NSF Innovation Corps (I-Corps) program and interviewed 100+ customers across three industries: pharmaceutical, biochemical and the oil field chemical industry. The outcomes from the I-Corps are: (1) we validated our product and market fit; (2) we found a $300milion market opportunity in generic SGLT2 antidiabetic drug industry; (3) we identified that we need to produce 1-5g LGA as customer sample (MVP: minimum viable product).