If you deprotonate you can get ringclosure, a problem with the Grignard route is that you can get ringclosure of the final acid if you use a acid-labile protecting group. You could use a benzyloxymethyl group, this can be removed by hydrogenation and can be put on with mild base like triethylamine and benzyloxymethylchloride. The nitril-route is more convinient. I wonder why you want to do this, cant you buy the acid? Or hydrolyze the corresponding lactone?