R1 is then removed by heating with dilute aqueous acid (e.g., 4N to 6N acid) as described above in connection with step (8) of Scheme I. A compound of Formula XI can then be converted in step (3) to a compound of Formula XIII by reaction with a suitable chlorinating agent such as thionyl chloride, phosgene, oxalyl chloride, phosphorus pentachloride, and the like, or preferably phosphorus oxychlori