Regioselective halogenation of pentono-1,4-lactones. Efficient synthesis of 5-chloro- and 5-bromo-5-deoxy derivatives

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.