using System;

using System.Collections.Generic;

using System.Linq;

using Newtonsoft.Json.Linq;

public class Program

{

    public static void Main()

    {

        string json = @"

            {

              ""CustomData"": [

                {

                  ""Wrapper"": [

                    {

                      ""OptionalDataSet1"": [

                        {

                          ""ItemA"": ""Basic string""

                        },

                        {

                          ""ItemB"": ""Another basic string""

                        }

                      ]

                    }

                  ]

                }

              ]

            }";

        Dictionary<string, string> optionalDataSet1 = Deserialize(json);

        foreach (var kvp in optionalDataSet1)

        {

            Console.WriteLine(kvp.Key + ": " + kvp.Value);

        }

    }

    public static Dictionary<string, string> Deserialize(string json)

    {

        return JObject.Parse(json)

            .SelectToken("CustomData[0].Wrapper[0].OptionalDataSet1")

            .Children<JObject>()

            .SelectMany(jo => jo.Properties())

            .ToDictionary(jp => jp.Name, jp => (string)jp.Value);

    }

}