Some of those purchases were at the Benson, a condo tower under construction on Madison Avenue near 80th Street, where eight of the 15 full-floor units have found takers since sales began in September. A 15th-story apartment at the Naftali Group project went into contract in early December at the asking price of $14.15 million, the second-costliest deal in Manhattan for that week, according to Olshan.