using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{   

    public static void Main()

    {

        // your dictionary of items

        var dict = new Dictionary<int, string>();

        dict.Add(0, "Zero");

        dict.Add(2, "Two");

        dict.Add(4, "Four");

        // as suggested by Jon Skeet, create a HashSet to be more performant

        var hs = new HashSet<string>(dict.Values);

        // list of unfiltered items

        var list = new List<dynamic>()

        {

            new { Id = 0, Name = "Zeroth", PropertyYouWantToCheck = "Zero" },

            new { Id = 1, Name = "First", PropertyYouWantToCheck = "One" },

            new { Id = 2, Name = "Second", PropertyYouWantToCheck = "Two" },

            new { Id = 3, Name = "Third", PropertyYouWantToCheck = "Three" },

            new { Id = 4, Name = "Fourth", PropertyYouWantToCheck = "Four" },

        };

        // LINQ query to filter the list

        var filteredList = list.Where(i => hs.Contains(i.PropertyYouWantToCheck));

        // output the name of the filtered items

        Console.WriteLine(string.Join(", ", filteredList.Select(fl => fl.Name)));

    }

}