Alkoxy(alkylthio)-4-hydroxy-2H-pyran-2-ones readily react with electrophiles to give substitution products at C-3. Hard electrophilic reagents replace hydrogen both in position 3 and in position 5 of the pyran ring. Methylation of 6-alkoxy(alkylthio)-4-hydroxy-2H-pyran-2-ones with diazomethane leads to formation of O- and N-methyl derivatives.