SK Inc. agreed to sell its controlling stake in semiconductor wafer maker SK Siltron to Doosan Corp. for about 2.3 trillion won ($1.6 billion), freeing up cash as the conglomerate reshapes its portfolio and invests in new growth businesses. SK’s board approved the sale of its 70.6 percent stake Friday, clearing the way for the two companies to sign a share purchase agreement. Doosan was named preferred bidder in December. The stake being sold comprises 51 percent held directly by SK and another