A process for mono-N-beta hydroxylation of cyclene for the production of a N-beta-hydroxyalkyl-l, 4, 7, 10-tetraazacyclododecane of formula I where Rl is and R2 and R3 are, iadependently of one another, a hydrogen atom, together with the carbon atoms they are bonded to a 4-, 5-, 6-or 7-niembered cycloalkyl ring which optionally can be interrupted by 1 to 3 oxygen atom(s), or a C1-C12 alkyl radical which optionally is substituted with 1 to 3 C1-C6 alkyl groups or 1 to 3 hydroxy groups, whereby the optionally present hydroxyl radicals are optionally present in protected form, which comprises reacting 1,4,7, 10-tetraazacyclodecane, optionally in the form of a salt, with, an epoxide of formula 11, in which R2 and R3 have the above-indicated meanings, in the presence of 0.8-1.1 mol of lithium salt relative to one mol of cyclene at a temperature of from 40-150°C, and working up the reaction in aqueous form.
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