Nobody except OP can really answer why it needs to be United, but if a UA-marketed and sold codeshare flight is allowed, UA 7983 (which is ANA 105) is LAX-HND leaving at 1:20 AM. Almost any flight from Europe the previous day should be able to connect to it, even if it is a double connection in EWR or elsewhere.
Likewise, probably any UA flight from Europe to ORD could connect to UA 7991 (All Nippon 111 @ 5:25 PM) to Tokyo-Haneda.