Tax Breaks on corporate stock purchases: There was an extension of a tax break on the purchase of stock after 9/27/10 and before 1/1/12

Apparently if you but stock of a small corp (under $50 MM assets) during the above referenced time frame, and then hold the stock for five years, when you subsequently sell the stock, there is no tax on the gain but with a cap of 10 Xs the basis or $10 MM. Also exempt from AMT. Can anyone advise what section of the IRS code covers this? Would this apply to the stock purchase of a sub s corp?