Compounds of Formula (I) where X is N may optionally be prepared by converting a compound of Formula (IXa) or (IXb) to a compound of Formula (Xa) or (Xb) where W is ???C(Y)???X3 where X3 is a leaving group and Y is ???O or ???S. In one example, (IXa) or (IXb) is reacted with triphosgene to form (Xa) or (Xb) where W is ???C(O)