Two top aides to Boston Mayor Martin J. Walsh have been convicted by a federal jury for trying to coerce organizers of the Boston Calling music festival into hiring union workers. Kenneth Brissette, the city's director of tourism, was found guilty of extortion and conspiracy to commit extortion. Timothy Sullivan, chief of intergovernmental affairs, was found guilty of conspiracy to commit extortion. Judge Leo Sorokin had thrown out the charges after prosecutors admitted they could not prove the two men personally benefited from the festival hiring union workers. But Sorokin's decision was reversed by an appellate court, and at trial, prosecutors argued that the men's boss, Walsh, benefited politically from the festival hiring union workers.