A convenient synthesis of 4-benzyl-2-(2-(4-oxo-2- thioxothiazolidin-5-ylidene)ethyl)-2H-1,4-benzoxazin- 3(4H)-ones and 5-(2-(4-benzyl-3-oxo-3,4-dihydro-2H- 1,4-benzoxazin-2-yl)ethylidene)thiazolidine-2,4-diones