The present invention relates to the use of a compound containing a moiety of formula (I) as a reagent for linking a compound of formula R1—H which comprises a first functional moiety of formula F1 to a second functional moiety of formula F2 wherein X, X′, Y, R1, F1 and F2 are as defined herein. The present invention also provides related processes and products. The present invention is useful for creating functional conjugate compounds, and specifically conjugates in which at least one of the constituent molecules carries a thiol group.