Simplified Synthesis and Structural Characterization of Ethyl 2,2′-Spirobi[Chromene]-3-Carboxylate via Spectroscopy and Single-Crystal X-ray Analysis

Abstract Chromene-based spiroketals are valuable structural motifs in medicinal and synthetic organic chemistry; however, their reported syntheses typically require multi-step routes and harsh reaction conditions. In this work, a simple, efficient, and cost-effective one-pot method for the synthesis of ethyl 2,2′-spirobi[chromene]-3-carboxylate is presented. The compound was obtained via the acid-catalyzed condensation of salicylaldehyde with ethyl acetoacetate in methanol using only a few drops of H 2 SO 4 , affording the spiroketal framework in a single step under mild conditions. Structural elucidation was performed using comprehensive spectroscopic techniques, including FTIR, HR-MS, and 1D/2D NMR analyses. Given the novelty of the compound, detailed 2D NMR (HSQC, HMBC, and COSY) studies were carried out to unambiguously assign proton and carbon resonances within the spiro-linked chromene units. The molecular structure was further confirmed by single-crystal X-ray diffraction, providing definitive evidence of the spiro-fused architecture. Elemental analysis supported the purity and composition of the synthesized product. This streamlined synthetic strategy offers an attractive alternative to conventional routes and may provide a useful platform for the development of new chromene-based spiroketal derivatives. Graphical Abstract