A process is provided for preparing compounds having the general formula I wherein R is a range of organic groups and X is a leaving group. The process comprises reacting a compound of formula II with a water-removing reagent. When X is halogen or a sulfonate, the compound of formula I may be prepared by reacting a compound of the formula III with a halogenating agent or a sulfonylating agent. Alternatively, when X is halogen, the compound of formula I can be prepared by reacting a compound of the formula IV where R2 and R2 are defined organic groups, with a compound of the formula halogen-C(—O)—O—C1-C8alkyl, halogen-C(—O)—O-aryl or halogen-C(—O)—O-benzyl.