Conn. Gen. Stat. § 12-39w
Claims for refund where results of civil audit, investigation, examination or reexamination have become final.
(2) A taxpayer may file a claim of refund for any period for which the results of any civil audit, investigation, examination or reexamination conducted by the commissioner have become final by operation of law or for which the associated administrative or judicial rights of appeal have been exhausted, provided such claim is filed not later than six months after the date such results become final by operation of law or the date such rights of appeal are exhausted, as applicable and whichever is later.
(b) The provisions of subsection (a) of this section shall not affect claims for refunds authorized under the provisions of sections 12-226 , 12-704 and 12-727 .