The application is directed to compounds of Formula I-Aand pharmaceutically acceptable salts and solvates thereof, wherein , R1a—R3a, R4, Y and Za are defined as set forth in the specification. The invention is also directed to use of compounds of Formula I-A to treat disorders responsive to the modulation of one or more opioid receptors, or as synthetic intermediates. Certain compounds of the present invention are especially useful for treating pain.
