The underlined portion needs to function adverbially as a purpose clause. It answers the question why or for what purpose?
 I use two alarm clocks not to oversleep.
Q: Why do you use two alarm clocks?
A: So (that) I don't oversleep.
A: (So as) not to oversleep.
[2a] A tiger was reported to have escaped from the zoo. (passive)
[2b] They reported a tiger to have escaped from the zoo. (active + passive)
[3a] in school means during
[3b] at school refers to a location
Does that help?