Use .net core project with moniker net451 in classic class library

Why I'm not able to use class library targeting to .net core with moniker net451 in classic .net class library (.net framework 4.5.1)?

Edit: When I try add reference in Class library project for .net framework 4.5.1 (full 451 for next time) to .net core project following error showed up.

Here is config.json from .net core project Idea7.Entity:

{
  "version": "1.0.0-*",
  "description": "Idea7.Entity Class Library",
  "authors": [ "Sebastian Bušek" ],
  "tags": [ "" ],
  "projectUrl": "",
  "licenseUrl": "",

  "frameworks": {
    "net451": { },
    "dotnet5.4": { }
  },
  "dependencies": {
    "Microsoft.CSharp": "4.0.1-beta-23516"
  }
}

For now, it's not possible to reference .net core class library in .net framework 4.5.1 class library project in Visual Studio by click "Add reference"; but you can add reference to builded *.dll.

To do that, you need to do few simple steps:

• Check Produce outputs on build in project properties (Build menu item)
• In solution directory is "artifacts" folder and it contains all builded .net core class libraris

Little bit flaffy, but working...