using System;

using System.Collections.Generic;

using System.Linq;

using Newtonsoft.Json;

public class Program

{

    public class Demo {

        public int foo {get; set;}  

    }

    public class Demo2 : Demo {

        public string bar {get; set;}

    }

    public static void Main()

    {

        Demo2 test = new Demo2() {

            bar = "abc",

            foo = 1

        };

        Demo test2 = JsonConvert.DeserializeObject<Demo>(JsonConvert.SerializeObject(test));

        Demo2 test3 = (Demo2)test2;

    }

}