IRC § 1361(b)(3)
Qualified Stock Purchase and QSub Election
An S corporation buys all of the stock of a target for cash and short-term notes in a qualified stock purchase, then makes a QSub election so the target is treated as a qualified subchapter S subsidiary.
Treas. Reg. § 1.1361-4(a)(2)(ii), Example 1 • Qualified Subchapter S Subsidiaries