When you're in shul the davening is up to "ashrei" or "aleinu" one is supposed to say that along with the tzibbur. So I was wondering what if I was in middle of davening say in the middle "uva letzion" and the tzibbur is up to "aleinu": Should I stop and say aleinu and go back to where I was up to, or should I just continue davening?
Answer:
Although it is correct that one should say "aleinu" with the congregation, if one is saying "uva le-tzion" one should not skip to "aleinu," but rather continue to daven according to the order.
This can be derived from several poskim, who mention skipping "ashrei" and "la-menatzeiach" for the purpose of saying the kedushah of "uva le-tzion" with the congregation. No mention is made of skipping for the purpose of saying "alienu" with the tzibbur, and the implication is that one should continue to daven according to the order.