Robert Greifeld, chief executive of Nasdaq Stock Market., is closing this week on his first trans-Atlantic takeover. Next comes trying to make the most out of Plan B.

With exchanges around the world racing to merge, the 50-year-old Greifeld made a brash play for the London Stock Exchange in 2006 but was forced to retreat when it became obvious that the storied market wouldn't succumb to Nasdaq's hostile bid.