Engine cranks but does not start and lost four out of six quarts of oil

Hello,

First of I am assuming you have added proper amount of oil.
Did the vehicle loose all of that oil all of a sudden, or has it been running low for sometime?
If the vehicle shut down due to lack of oil/oil pressure, you could have damaged engine internals.

Is the check engine light illuminated? Sometimes in no start, there is a fault code. Which can point us to the right direction.

https://www.2carpros.com/articles/bmw-obd1-1995-and-earlier-code-definitions-and-retrieval-procedure

https://youtu.be/vMwTzURWXmk

If the engine cranks but does not start it could be either for no spark or no fuel.
I would suggest first check for codes then go from there.

Please let me know what you find.

Thank you.