Is it unreasonable to expect students to read the lecture notes before attending the first class?
In my opinion,  yes it is unreasonable.

Disclaimer: I am a student in the Netherlands, different universities and countries might work differently.

In all the courses I've followed I can't remember a single one that expected me to prepare for the first class. Usually the first half of the first lecture of a course is dedicated to explaining how the course works, what is expected of you, and anything else related to organization. Most students, including myself, usually don't even register in the online environment where the teaching material is posted before the first lecture.

You could argue that maybe this shouldn't be the case, and that students should be more diligent. And naturally, it is up to you whether you want to take this view and potentially punish students who didn't prepare. Practically though, most students are probably just going to miss it, or skip it. 

If you do decide to have students prepare for the first lecture, make sure to clearly note this in the course guide/emails/online announcements. And also note the potential consequences for students who do not prepare.