Treatment of unprotected d-ribono, d-arabinono and d-xylono-1, 4-lactones with either thionyl chloride or thionyl bromide in dimethylformamide led to 5-chloro-or 5-bromo-5-deoxy derivatives in 70%–95% yields. Under the same conditions, d-lyxono-1, 4-lactone resulted in the 2-halogeno compounds.