The work takes advantage of an important feature of flow chemistry, whereby the generation of a transient species (or reactive intermediate) can be followed by a transfer step into another chemical environment, before the intermediate is reacted with a coupling partner. This concept is successfully applied to achieve a room temperature sp2-sp3 cross coupling of boronic acids with diazo compounds, these latter species being generated from hydrazones under flow conditions using MnO2 as the oxidant.