When replicating between different major versions (i.e. 5.1 and 5.6), the slave should generally be newer than the master. So while I have not tested this case specifically, I doubt it will work.
It may be possible to do the reverse; a 5.1 master and a 5.6 slave, but generally only one major jump in version is supported (i.e. from a 5.1 master to a 5.5 slave). Take a look at the below link to the manual for more details: