Complex sentence: He was associated with the Whitney Museum of American Art in New York City for many years, first as a curator in the 1930s and finally as Director of the museum from 1958 until 1968.
Split into simpler sentences: He was associated with the Whitney Museum of American Art in New York City for many years. First as a curator in the 1930s and finally as Director of the museum from 1958 until 1968.