The application is directed to compounds of Formula I
and pharmaceutically acceptable salts, prodrugs, and solvates thereof, wherein G, R
2
-R
5
, and
are defined as set forth in the specification. The invention is also directed to use of compounds of Formula I as synthetic intermediates or to treat disorders responsive to the modulation of one or more opiopid receptors. Certain compounds of the present invention are especially useful for treating pain.