skill in the art see wuts peter g m and greene theodore w greene 39 s protective groups in organic synthesis 4 th edition wiley 2006 print isbn 978 0 471 69754 1 online isbn 9780470053485 bromine is a preferred leaving group bromine chlorine and iodine can be added by reacting the compound of formula viii with hydrogen bromide hydrogen chloride or hydrogen iodide respectively this reaction is generally carried out in a solvent such as acetic acid acetic anhydride or sulfuric acid preferably a mixture of acetic acid and acetic anhydride at a temperature from about 0 u00b0 c to about 60 u00b0 c preferably from about 20 u00b0 c to about 30 u00b0 c mesylate triflate tosylate and brosylate groups can be added by reacting the compound of formula viii with respectively rnesyl chloride trifluoromesyl chloride tosyl chloride and brosyl chloride in a solvent e g an ether such as diethyl ether dipropyl ether or thf toluene or an alkane such as heptane hexane or cyclohexane or a mixture of one or more of the foregoing solvents with a mixture of toluene and thf being preferred at a temperature from about u2212 10 u00b0 c to about 00 u00b0 c preferably from about 0 u00b0 c to about 20 u00b0 c in the presence of a base such as triethylamine n n diisopropylethylamine or pyridine alternatively this reaction can be conducted in a.