Although regulators have yet to approve the sale of Boston-based Caritas Christi Health Care to a New York investment firm, the hospital chain is already taking steps to expand by buying other community hospitals. Caritas chief executive Ralph de la Torre has been quietly courting area hospitals about potential mergers in a bid to expand the system of six Catholic hospitals in Eastern Massachusetts, according to several healthcare executives with knowledge of the talks. People who know de la Torre say he wants to create a chain large enough to compete in markets outside Boston with nonprofit Partners HealthCare, the Boston Globe reports.