If you want to use a variable value as key of your map, then you should wrap your key with parenthesis. It makes key to be considered as expression instead of String literal.
String keyVar = "mykey"
def map0 = [keyVar : 12]
assert map0.keyVar == 12
assert !map0.mykey
def map1 = [(keyVar) : 12]
assert map1.mykey == 12
assert !map1.keyVar