You can use the System.Management and the WMI class win32_directory to
compress a folder.

string dirName = "c:\\\\someFolder";
string objPath = "Win32_Directory.Name=" + "\"" + dirName + "\"";
using (ManagementObject dir= new ManagementObject(objPath))
{
ManagementBaseObject outParams = dir.InvokeMethod("Compress", null,
null);
uint ret = (uint)(outParams.Properties["ReturnValue"].Value);
if(ret == 0)
Console.WriteLine("Success");
else Console.WriteLine("Failed with error code: {0}", ret);
}