Lisa Dennison has resigned as director of the Guggenheim Museum and will take a job at Sotheby’s. “She is not the first museum director to join Sotheby’s. Over the years it has hired Richard E. Oldenburg, the former director of the Museum of Modern Art, and Charles S. Moffett, a director of the Phillips Collection in Washington, among others. Their connections to rich collectors and knowledge of art can make them highly desirable as business-getters for an auction house.”