* Hillshire to buy Pinnacle Foods for $6.6 billion
* IBM CEO says company is facing a "rocky time": NYT
* Ukraine situation remains in focus after referendum
* Futures up: Dow 51 pts, S&P 6.9 pts, Nasdaq 18.5 pts (Updates prices, adds Tesaro news)
By Ryan Vlastelica
NEW YORK, May 12 (Reuters) - U.S. stock index futures pointed to a higher open on Monday, putting the S&P 500 within striking distance of record levels, though geopolitical concerns in the Ukraine could cap gains.
* In Ukraine, pro-Russian rebels voted in favor of self-rule in eastern regions of the country in a referendum dismissed by Kiev and Western governments as illegal. Separately, the European Union is set to step up pressure on Russia by taking steps to extend sanctions to companies, as well as individuals.
* In the latest deal news, Hillshire Brands Co agreed to buy Pinnacle Foods Inc for about $6.6 billion. Pinnacle jumped 20.5 percent to $36.70 in premarket trading while Hillshire was up 3 percent at $38.05.
* The board of Allergan rejected an unsolicited proposal from Valeant, saying it significantly undervalued the company.
* Separately, the head of research at Pfizer Inc pressed the case for the company's plan to buy AstraZeneca for $106 billion, saying a deal wouldn't disrupt drug research. U.S. shares of Astra rose 1.1 percent to $78.11 before the bell while Dow component Pfizer was up 0.6 percent at $29.20.
* Virginia Rometty, chief executive of IBM Corp, told the New York Times the company was facing a "rocky time" but has a clear vision on how to pursue another generation of growth.
* S&P 500 futures rose 6.9 points and were above fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures added 51 points and Nasdaq 100 futures rose 18.5 points.
* The S&P 500 has found support at its 50-day moving average, bouncing off that level on Friday and ending right above its 14-day moving average, a sign of improving positive momentum. The benchmark index is about 1 percent from a record intraday high reached on April 4.
* Tesaro Inc shares jumped almost 21 percent to $29 in premarket trading after the company said its experimental drug for the prevention of chemotherapy-induced nausea and vomiting met the main goal in a third late-stage trial.
* Wall Street was volatile last week, with the Dow ending at a record close on Friday but the Nasdaq suffering its biggest weekly percentage decline in a month. In addition, the Russell 2000 of small-cap companies flirted with correction territory, dropping nearly 10 percent from its all-time closing high. (Editing by Bernadette Baum)