Case insensitive pandas.concat

Case insensitive pandas.concat

How would I perform a case insensitive pandas.concat?
df1 = pd.DataFrame({"a":[1,2,3]},index=["a","b","c"])
df2 = pd.DataFrame({"b":[1,2,3]},index=["a","b","c"])
df1a = pd.DataFrame({"A":[1,2,3]},index=["A","B","C"])
pd.concat([df1, df2],axis=1)
a b
a 1 1
b 2 2
c 3 3
but this does not work:
pd.concat([df1, df1a],axis=1)
a A
A NaN 1
B NaN 2
C NaN 3
a 1 NaN
b 2 NaN
c 3 NaN
Is there an easy way to do this?