Is there a general radio frequency in Class G for broadcasting intentions?
I'm not aware of any regulation or AIM entry that specifies what frequency to be on.

I use the UNICOM frequency of the nearest airport when I'm out looping because I consider it to be the frequency most likely to be used by traffic near me.

It also has a mild safety benefit -- if something on my plane were to break, I'd already be on the right frequency for the airport I'm about to inhabit.