in toluene to a soln. of O(B(OAc)2)2 benzothiazoline (molar ratio 1:1) was aded; amixture was refluxed for 12 h, acetic acid liberated being removed azeotripically; concn., residue was dried at 60-65°C/0.05 torr; repeatedly washed with dry hexane; elem. anal.;