Douglas Marr senior vice president of Keliher Real Estate has just sold 245 Commonwealth Ave. in the city's Back Bay for $6 million. This 5-story brick and brownstone 8 unit building is being gutted and converted to a single family, the property is 8,950 s/f with 6 parking space located on the Sunnyside of Commonwealth Ave. between Fairfield and Gloucester St. The seller was Mainsail LLC and the buyer is K. Properties LLC.