it comprises a preparation process of montelukast from a new intermediate compound of formula , which is previously prepared by reaction of the corresponding sulfonate with 1 - cyclopropyl ) methanol . compound is reacted with a grignard reactant to convert the ester group into a tertiary alcohol , followed by conversion of the primary alcohol into a sulfonate , substitution of the sulfonate group by a cyano group , and finally transforming the cyano compound to the carboxilic acid compound by a hydrolysis reaction to afford montelukast . montelukast can also be prepared by a hydrolysis reaction of the corresponding amide . it also comprises new intermediate compounds useful in such preparation process .