Transformation of glucose to quinoxalines. (A) Carbon distributions of glucose for the reaction with different additive. Reaction conditions: glucose (0.5 mmol), H₂O (20 mL), 180ºC, 5 h, N₂ (2 MPa), the amount of amine additive (aniline and o-PDA) was based on total amino groups (4 mmol). ^a KOH (0.15 mmol) was added. (B) The composition of identified products obtained from glucose transformation in the presence of o-PDA and KOH. (C) The composition of total formed quinoxalines. The reaction progression monitored by ¹H NMR (D) and ¹³C NMR (E). (F) Proposed plausible reaction pathways for transforming glucose into quinoxalines in the presence of o-PDA. Cyclic forms of the sugars are omitted for clarity. (G) Synthesis of various 2-methylquinoxalines via the proposed reaction with a minimal KOH additive and their potential for manufacturing high-value bioactive compounds. The values in the parentheses indicate the percentage of the corresponding 2-methylquinoxalines in total formed quinoxaline products.