I'm not sure what this can be called the easiest way, but if you have ReSharper , you can use it Copy type to copy classes / interfaces / structures with control over the namespace into which the copy is copied and the name in the copy, which means that if you copy a class with 5 constructors, the copy will be completely renamed to match the name of the new class.
However, depending on what you are trying to achieve, using the Extract Interface or Extract Superclass may be a better option.