Someone

using System;

namespace Program {
 class Program {        
  static void Main() {
   string s1 = "Cadena    con     espacios", s2=""; bool x = true;    
   foreach (char c in s1){if(c!=32){s2+=c;x=true;continue;}if(x){s2+=c;x=!x;}}      
   Console.WriteLine(s2);
   Console.ReadLine();
  }
 }
}