I and up writing my own compose file to mimic OSX, here it goes to help someone in need. Note that this is the main used speacial chars for Brazilian Portuguese, maybe you have other need but it's easy to add your own keys.
Create a .XCompose file on your home with the following content:
#this include all the default compose keys on the file
include "%L"
<Multi_key> <c> : "ç"
<Multi_key> <C> : "Ç"
<Multi_key> <e> <a> : "á"
<Multi_key> <e> <A> : "Á"
<Multi_key> <e> <e> : "é"
<Multi_key> <e> <E> : "é"
<Multi_key> <e> <i> : "í"
<Multi_key> <e> <I> : "Í"
<Multi_key> <e> <o> : "ó"
<Multi_key> <e> <o> : "Ó"
<Multi_key> <e> <u> : "ú"
<Multi_key> <e> <U> : "Ú"
<Multi_key> <n> <a> : "ã"
<Multi_key> <n> <A> : "Ã"
<Multi_key> <n> <o> : "õ"
<Multi_key> <n> <O> : "Õ"
<Multi_key> <i> <e> : "ê"
<Multi_key> <i> <E> : "Ê"
<Multi_key> <i> <o> : "ô"
<Multi_key> <i> <O> : "Ô"
I just adapted the ç to make it a keystroke shorter.