The general procedure for the synthesis of 5-chlorobenzo[d]thiazole from 2,5-dichlorobenzothiazole is as follows: Pd(OAc)2-PPh3, Pd2(dba)3-tbpf, Pd2(dba)3-DavePhos, Pd2(dba)3-P(t-Bu)3, Pd2(dba)3-XantPhos or Pd(OAc)2 -XPhos as catalyst systems. First, anhydrous THF (13.2 mL) was degassed by bubbling argon for a few minutes, followed by the addition of Pd(OAc)2 (7.2 mg, 0.033 mmol, 5 mol%) and PPh3 (17.7 mg, 0.132 mmol, 20 mol%) and stirring the mixture for 30 minutes at room temperature. Next, halogenated heterocycles (0.66 mmol), TMEDA (0.130 g, 1.12 mmol, 1.7 eq.) and NaBH4 (42.4 mg, 1.12 mmol, 1.7 eq.) were added sequentially. The reaction mixture was stirred at room temperature or heated under argon protection at 65 °C for an appropriate time. After completion of the reaction, the residue was dissolved in brine and extracted with ethyl acetate. The organic phase is separated, dried and the solvent is evaporated, and finally the residue is purified by fast chromatography (a solvent mixture of petroleum ether and ethyl acetate) to give the pure hydrodehalogenated heterocyclic product.
