the amount received from such disposition shall be treated as an amount received in part or full payment for the stock sold or redeemed. In the case of a sale, only the stock interest need be terminated. In determining whether an entire stock interest has been terminated under section 306(b)(1)(A), all of the provisions of section 318(a) (relating to constructive ownership of stock) shall be applicable. In determining whether a shareholder has terminated his entire interest in a corporation by a redemption of his stock under section 302(b)(3), all of the provisions of section 318(a) shall be applicable unless the shareholder meets the requirements of section 302(c)(2) (relating to termination of all interest in the corporation). If the requirements of section 302(c)(2) are met, section 318(a)(1) (relating to members of a family) shall be inapplicable. Under all circumstances paragraphs (2), (3), (4), and (5) of section 318(a) shall be applicable.
26 C.F.R. §1.306-2