Synthesis and Characterization of cis-/trans-(±)-3-Alkyl-3,4-dihydro-6,7-dimethoxy-1-oxo-1H-isochromene-4-carboxylic Acids

A series of new 3-alkyl substituted cis- and trans-(±)-3,4-dihydro-6,7-dimethoxy-1-oxo-1H-isochromene-4-carboxylic acids (cis-/trans-1–3) was synthesized through the reaction of 6,7-dimethoxyhomophthalic anhydride with aliphatic aldehydes of varying chain lengths. Their structure and configuration were elucidated using spectral methods, including 1H, 13C, DEPT-135 NMR, FTIR, UV-Vis, and HRMS analyses. A deductive conformational analysis was performed for determining the preferred conformations in solution and to explain the observed vicinal coupling constants.