The invention relates to an improved process for the preparation of an advanced synthetic intermediate of ACE inhibitors. In one aspect, the present invention is based on a novel process for the preparation of an aldehyde of formula (I), wherein (N)PrG is a protected amino group, R is an alkyl or aralkyl group and X1-4 are each independently H or a non-reacting substituent, which comprises hydroformylation of an α-olefin of formula (II), by reaction with syngas (CO/H2) in the presence of, as catalyst, a group VIII transition metal complex of a phosphorus-containing ligand. Aldehyde (I), the product of linear hydroformylation, is formed in preference to aldehyde (III). In another aspect of the invention, α-olefin (II) is a novel composition. The process to convert (II) to (I) enables an efficient manufacturing route to MDL 28,726 and analogues.