Drugstore chain Walgreen Co. says it will spend $6.7 billion to buy a stake in health and beauty retailer Alliance Boots. The Deerfield, Ill., company plans to spend about $4 billion in cash and more than 83 million shares for a 45 percent ownership stake, and it has an option to buy the rest of the company. Alliance Boots runs more than 3,300 health and beauty retail stores in 11 countries, and its pharmaceutical wholesale business supplies pharmacies, doctors and other providers in 21 countries. Walgreen is the largest U.S. drugstore operator. It has an option to buy the rest of Alliance Boots in about three years in a deal valued at about $9.5 billion.