It’s not long into the new musical Darling Grenadine, after a brief direct address to the audience by Adam Kantor’s ingratiating lead character, Harry, that the first song comes, but it takes till the top of the second act to get to the song that gives the show its bizarre title. It’s an ode to the pomegranate syrup that goes into a Shirley Temple, and by that time what began as a romance of struggling artists in New York City has found an unexpected path through the shopworn trappings of such tales.