Catalysis of the reaction: 2,4,6/3,5-pentahydroxycyclohexanone = 3D-3,5/4-trihydroxycyclohexane-1,2-dione + H2O.
2,4,6/3,5-pentahydroxycyclohexanone hydro-lyase (3,5/4-trihydroxycyclohexa-1,2-dione-forming)