Copper and zinc complexes of kojic acid and related ligands

M(II) (M = Cu, Zn) complexes of kojic acid (1, 2) have been synthesised, but characterisation was hampered by their lack of solubility. Related metal derivatives (5, 6) of benzyl-protected comenic acid (4), an oxidised variant of kojic acid, have been prepared, and the structures of 5·H<inf>2</inf>O·3DMSO (5a) and 6·2H<inf>2</inf>O (6a) were determined. The menthyl ester of O-benzyl comenic acid (7) has been prepared, but complete de-protection proved difficult. 3-Hydroxy-6-menthoxyacetyloxymethyl-4-pyrone (9) was prepared along with its M(II) derivatives (10, 11), though both were of low solubility; 10 forms soluble 1:1 adducts with pyridine (12) and 2,2′-bipyridine (13). Menthyl-3-oxo-butanoate (14) has been prepared along with its copper complex (15), whose structure has been determined. Included in the report are the structures of 4·DMSO (4a), 4·MeOH (4b), 4·THF (4c) and 9.