Greenfield shares rose $1.26, or 7.9 percent, to $17.24. In the past year, the stock has ranged from $10.25 to $17.44.
Greenfield said it plans to terminate a merger agreement made in June with Quadrangle, which would have given shareholders $15.50 per share. The proposed transaction was worth about $407.9 million based on the company's 26.3 million outstanding shares as of May 2.
According to the agreement, Quadrangle has three days to increase its offer, Greenfield said. Terminating the agreement would cost Greenfield $5 million.
The new offer is not contingent on financing, Greenfield said.