A company that Rosneft recently sold to a U.S. entrepreneur bought Yukos' international unit at a forced auction Wednesday, as former Yukos managers vowed to pursue a legal challenge to salvage part of what was once the country's largest oil firm. Promneftstroi, recently acquired by businessman Stephen Lynch, won the unit, Yukos Finance, for 7.8 billion rubles ($305 million) after five minutes of bidding. The winning bid fell well below the $2.7 billion value that former Yukos managers place on the unit, and was just 240 million rubles ($9 million) above the starting price.