The invention relates to methods of preparing compounds of formula (II) wherein Z represents —OR1 or N(R2)R2a—, where R1 is lower alkylene (C1-C6), R2 is lower alkyl or H and R2a is lower alkylene (C1-C6) or H; Q is absent when R2a is H and is otherwise selected from the group consisting of H, —OH and protected forms of —OH; one of X and Y is halogen and the other is —OSO2R3, where R3 is selected from the group consisting of lower alkyl (C1-C6), phenyl and CH2phenyl. The method comprises the steps of: (a) reacting a compound of formula (I) with aziridineethanol or a 2-[(2-haloethyl)amino]ethanol in the presence of a metal halide, to form a compound of the formula (III) wherein one of X and E is halogen and the other is hydroxy, and (b) reacting the compound of formula (III) with an alkyl- or arylsulfonyl halide or alkyl- or arylsulfonyl anhydride to obtain a compound of the formula (II). The invention also relates to methods of preparing compounds of formula (IV) from the compounds of formula (II) so obtained, and to novel compounds of formula (IIb) useful as intermediates in these methods.