First of all your class declaration is incorrect.
According to the C++ Standard (9.2 Class members)
1 The member-specification in a class definition declares the full set of members of the class; no member can be added elsewhere. Members of a class are data members, member functions (9.3), nested types, and enumerators.
Secondly according to paragraph #2 of section 7.2 Enumeration declarations
An opaqueenum- declaration declaring an unscoped enumeration shall not omit the enum-base.
Also if a enum is declared as private its enumerators are also private.