Studies on Condensed Systems of Aromatic Series. XVII: Synthesis of 5- and 7-Chloro-2-methylbenzothiazoles and 2, 5- and 2, 7-Dimethylbenzothiazoles@@@5-,7-Chloro-2-methylbenzothiazole及び2,5-,2,7-Dimethylbenzothiazoleの合成