Compounds of the general formula (I)
in which:-
R₁ represents a hydroxyl protecting group; and
R₂ represents a hydrogen or halogen atom, an azido group, a C₁₋₃ alkyl group, a group (CH₂)mOR₃ wherein m is zero or one and R₃ represents a hydrogen atom or a hydroxyl protecting group, an azidoethoxy group, a protected hydroxyethoxy group or a group XR₄ in which X is an oxygen atom or the group S(O)n in which n is zero, 1 or 2 and R₄ represents a C₁₋₅alkyl, C₃₋₇ cycloalkyl or phenyl group or when X is oxygen or sulphur then R₄ may also represent the group AlkNR₅R₆ in which Alk represents a C₂₋₆ straight or branched alkylene chain and R₅ and R₆ independently represent a hydrogen atom or C₁₋₄alkyl group or R₅ and R₆ together with the nitrogen atom to which they are attached form a pyrrolidino or piperidino ring or the group NR₅R₆ represents a protected amino group, or R₂ represents the group (CH₂)mNR₇R₈ in which m is zero or 1 and R₇ and R₈ independently represent a hydrogen atom or a C₁₋₄alkyl group or NR₇R₈ represents a protected amino group, or R₂ and the carbon atom to which it is attached represent a keto group or a ketal derivative thereof;
and acid addition salts of such compounds containing basic centres.