PhI(OAc)(2)-promoted rearrangement of the hydroxyl group: Ring expansion of 4-hydroxy-2-cyclobutenone to 2(5H)-furanone in comparison with ring cleavage of the alpha-hydroxycycloalkanone to the omega-formyl ester

Reaction of 4-hydroxy-2-cyclobutenones with PhI(OAc)(2) in 1,2-dichloroetha ne at reflux temperature gave rise to 5-acetoxy-2(5H)-furanones as a rearra nged product, formation of which is explained by ring cleavage of the once formed hypervalent iodine intermediate and following recyclization of the r esulting acyl cation with a carbonyl oxygen. Likewise, 5-methoxy-2(5H)-fura nones were obtained in better yields by using methanol as both a solvent an d a nucleophile. Extension of this reaction to simple 2-hydroxycycloalkanon es resulted in ring cleavage to methyl omega-formylalkanoates under milder conditions. In this case, the mechanism is explained by known glycol cleava ge with PhI(OAc)(2).