The uncatalyzed reactions of o-substituted aromatic aldehydes with 5, 5-dimethyl-1, 3-cyclohexanedione in DMF were studied. The condensation and addition reaction of o-substituted aromatic aldehydes (1) with 5, 5-dimethyl-1, 3-cyclohexanedione (2) afforded 3, 3, 6, 6-tetramethyl-4a-hydroxyl-9-aryl-1, 8-dioxo-2, 3, 4, 4a, 5, 6, 7, 8, 9, 9a-decahydro-1H-xanthene (3a-3d). However, treatment of o- hydroxyl-aromatic aldehydes with 5, 5-dimethyl-1, 3-cyclohexanedione under the same conditions afforded 3, 3-dimethyl-9-(5, 5-dimethyl-3- hydroxyl-2-cyclohexene-1-one-2-yl)-1-oxo-2, 3, 4, 9-tetrahydro-1H- xanthene (4a-4b). The crystal structures of 3a and 4a were determined by X-ray diffraction analysis.

Key words: AROMATIC ALDEHYDE, CONDENSATION REACTION, CRYSTAL STRUCTURE, CYCLOHEXANEDIONE P, ADDITION REACTION, XANTHENE P, ORTHO-SUBSTITUENT