Abstract: This invention relates in part to processes for producing one or more substituted or unsubstituted hydroxyaldehydes, e.g., 6-hydroxyhexanals, which comprise subjecting one or more substituted or unsubstituted alkadienes, e.g., butadiene, to reductive hydroformylation in the presence of a reductive hydroformylation catalyst, e.g., a metal-organophosphorus ligand complex catalyst, and hydroformylation in the presence of a hydroformylation catalyst, e.g., a metal-organophosphorus ligand complex catalyst, to produce one or more substituted or unsubstituted hydroxyaldehydes. The substituted and unsubstituted hydroxyaldehydes produced by the processes of this invention can undergo further reaction(s) to afford desired derivatives thereof, e.g., epsilon caprolactone. This invention also relates in part to reaction mixtures containing one or more substituted or unsubstituted hydroxyaldehydes as principal product(s) of reaction.