2,2':5,6-Di-O-iso­propyl­idene-2-C-hydro­xymethyl-D-talono-1,4-lactone

A second crystalline diacetonide, the title compound, C₁₃H₂₀O₇, has been isolated from the sequential treatment of D-tagatose with aqueous sodium cyanide, followed by acetone in the presence of acid. Structural ambiguities with regard to the size of both the lactone and ketal rings are resolved by the X-ray crystallographic analysis.

1,2:3,4-Di-O-isopropyl­idene-α-D-tagatofuran­ose

The crystal structure of diacetone tagatose, C₁₂H₂₀O₆, establishes the stereochemistry of the anomeric spiro­acetal as 1,2:3,4-di-O-isopropyl­idene-α-D-tagatofuran­ose. Mol­ecules are linked by O—H...O hydrogen bonds [O...O = 2.862 (2) Å] to form chains running parallel to the b axis.