(2 R,3 R)-1,4-Dioxa-spiro-[4.4]nonane-2,3-di-carb-oxy-lic and (2 R,3 R)-1,4-dioxa-spiro-[4.5]decane-2,3-di-carb-oxy-lic acids

The title compounds, C9H12O6 and C10H14O6, were formed by careful hydrolysis of the corresponding diethyl esters. Their single crystals were grown from an ethyl acetate/hexane mixture. Crystals of both compounds have monoclinic (P21) symmetry with a single mol-ecule in the asymmetric unit. Both crystal structures are very similar and display four -CO-OH⋯O=C(OH)- hydrogen bonds, forming a two-dimensional double-layered framework.