I have a ASP.NET Core 1.0 MVC app in solution X and I have some common projects (.net 4.5.2 class libs) in solution Y.
I want to reference the projects in solution Y
Many people have struggled with this issue and there is a long running thread on GitHub about it. Even the people using the latest RC3 build are reporting the same problem that you are having.
The only way I've been able to reference class library projects in an ASP.NET Core web application is to create both the web application and the class library projects in Visual Studio 2015 Update 2. And they all have to target .NET Framework 4.6.1.
I had to copy the code from my old class library projects to the new ones. But in the end I think I saved myself time by not having to mess with all the workarounds that don't seem to work for a lot of people.