The present invention relates to processes for preparing isoprene and mono-olefins comprising at least six carbon atoms. In one aspect, a process comprises (a) hydroformylating a mixed C4 olefin stream, wherein the mixed C4 olefin stream comprises 1-butene, 2-butene, and optionally isobutene, with a hydroformylation catalyst, wherein the hydroformylation catalyst comprises rhodium with monodentate organophosphorous ligand and optionally polydentate organophosphorous ligand, to produce a mixture comprising linear and branched C5 aldehydes; (b) separating the branched C5 aldehydes from the linear C5 aldehydes to provide a branched C5 aldehyde stream and a linear C5 aldehyde stream; (c) dehydrating the branched C5 aldehydes in the branched C5 aldehyde stream using a dehydration catalyst to form a stream comprising isoprene; (d) hydrogenating the linear C5 aldehydes in the linear C5 aldehyde stream to form a C5 alcohol stream; (e) dehydrating the C5 alcohols in the C5 alcohol stream with a second dehydration catalyst to form a C5 olefin stream; (f) hydroformylating the C5 olefins in the C5 olefin stream to generate a C6 aldehyde stream; (g) hydrogenating the C6 aldehydes in the C6 aldehyde stream to form a C6 alcohol stream; and (h) dehydrating the C6 alcohols in the C6 alcohol stream with a third dehydration catalyst to form a C6 olefin stream.