The application is directed to compounds of Formula I′-A and especially to compounds of Formula I-A and pharmaceutically acceptable salts and solvates thereof, wherein R1a-R5a, Y, Za are defined as set forth in the specification. The invention is also directed to use of compounds of Formula I′-A, and especially 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.