Dutchman Peter Bosz, who last season guided a young Ajax Amsterdam team to runner-up Europa League and Dutch Eredivisie finishes, is Borussia Dortmund’s new coach. He replacesThomas Tuchel, who left Dortmund last week after his relationship with the club’s board deteriorated — despite winning the German Cup and qualifying for the Champions League groupstage by finishing third in the Bundesliga. The 53-year-old Bosz signed a two-year contract.