Namespace alias in c++

I use c++11 while I need some classes from c++17 library. When using boost from which classes were added I wish to do the following:

#if __cplusplus < CPP17
using std::any = boost::any;  
#endif

Such alias is not allowed. While I can 'extend' std namespace by renaming original one it is a bad desision. Is there a clear way?