Disclosed herein is an improved, commercially viable and industrially advantageous process for the preparation of a substantially pure aliskiren intermediate, 5-oxo-4-(propan-2-yl)-tetrahydrofuran-2-carboxylic acid or a stereochemically isomeric form thereof. The intermediate is useful for preparing aliskiren, or a pharmaceutically acceptable salt thereof, in high yield and purity. In the preparation of Aliskiren, 5-oxo-4-(propan-2-yl)-tetrahydrofuran-2-carboxylic acid (also referred to as the y-butyrolactone acid) of formula II and its (2S,4S)-enantiomer of formula IIa: are key intermediates.
