Shareholders change directors of embattled Exolon. (Exolon-ESK Co.)

A shareholder group that includes a dissident director has ousted four common directors, including the chairman and chief executive officer, of Tonawanda-based Exolon-ESK Co.

The removal of the directors prompted Wacker Chemical Corp., which seeks to buy Exolon and take it private, to file a lawsuit Dec. 31 in Delaware court challenging the removal.

A central question of the lawsuit is whether Theodore Dann Jr., an Exolon director, violated an agreement he made earlier this year to vote in favor of the proposed merger with Wacker Chemical.

Dann is vice president and general counsel of Ferro Alloys Services Inc., a Niagara Falls company that owns 20.7 percent …