Ivan F. Boesky staked out a position in Carbide.

The New York investor and a group of companies that he controls said they hold the equivalent of a 6.6% stake in Union Carbide’s common shares. In a Securities and Exchange Commission filing, the Boesky group said it holds the equivalent of 4.5 million common shares, including 520,400 shares that may be acquired through call options. The group said it took its Carbide position “in connection with merger arbitrage and other investment activities.”