using System;
using System.Text.RegularExpressions;
using System.IO;
using System.Linq;
public class Test
{
	public static readonly Regex rxQuoted = new Regex(@"""([^""\\]*(?:\\.[^\\""]*)*)""");
	public static void Main()
	{
		// 1. Regex: \b(?:to\ background)\b, Match: N/A
		checkIt("to background", "I need to find a string in this sentence!");
		// 2. Regex: \b(?:to|background)\b, Match: to
		checkIt("\"to\" \"background\"", "I need to find a string in this sentence!");
		// 3. Regex: \b(?:to\ find)\b, Match: to find
		checkIt("\"to find\"", "I need to find a string in this sentence!");
	}
	public static void checkIt(string searchString, string sentence)
	{
		var lst = rxQuoted.Matches(searchString)
				.Cast<Match>()
				.Select(p => Regex.Escape(p.Groups[1].Value))
				.ToList(); 
	    var pattern = lst.Count > 0 ? 
				@"\b(?:" + String.Join("|", lst) + @")\b" :
				@"\b(?:" + Regex.Escape(searchString) + @")\b";
	    Console.WriteLine("Regex: " + pattern);

		Match match = Regex.Match(sentence, pattern);
		if (match.Success)
		{
    		Console.WriteLine("Match value: " + match.Value);
		}
	}
}