Multicylcle Constraints with TimeQuest

I am still learning the syntax and rules of TimeQuest but I believe your command should be like this:

set_multicycle_path -setup -end -from [get_pins reg1|clk] -to [get_pins reg2|*] 4

As indicated by altera example for two register path(TimeQuest design examples). Your example is more like that for one clk...

You must also be careful about multicycle validity. If your register is enabled every 4 clks it doesn't mean automatically that it is a valid case. If its D input is launched regularly every 4 clks then that is a valid case but if some other signals share the drive on thIs D input then it may not be valid.