The application is directed to a process for increasing the proportion of 7β-epimer in an 7α/7β-epimer mixture of a 7-substituted 6α,14α-ethenomorphinan or a 7-substituted 6α,14α-ethanomorphinan, and specifically of compounds of Formula (I), wherein G, R2-R4, and are defined as set forth in the specification. The application is also directed to a process for purifying the 7β-epimer from an 7α/7β-epimer mixture of a 7-substituted 6α,14α-ethenomorphinan or a 7-substituted 6α,14α-ethanomorphinan. The application is also directed to a process for preparing 7β-substituted compounds of Formula Vb wherein G and R2-R5 are defined as set forth in the specification.