contacting a compound of formula a or a salt thereof with a compound of formula b or a salt thereof b subjecting the compound of formula iii or a salt thereof to n deprotection and alcohol reduction conditions to provide a compound of formula iv c contacting the compound of formula iv or a salt thereof with a compound of formula v under reductive amination conditions to provide the compound of formula i or a salt thereof wherein each pg independently is a protecting group the addition conditions of step a comprise a base and a catalyst the non limiting examples of the base include sodium carbonate sodium bicarbonate potassium carbonate potassium bicarbonate potassium tert butoxide potassium tert pentoxide cesium carbonate lithium tert butoxide magnesium tert butoxide sodium tert butoxide potassium hydroxide and lithium hydroxide the non limiting examples of the catalyst include tetrabutylammonium hydrogen sulfate tetrabutylammonium fluoride tetrabutylammonium chloride tetrabutylammonium bromide tetrabutylammonium iodide 18 crown 6 and 15 crown 5 the addition conditions of step a further comprise a solvent the non limiting examples of the solvent include isopropyl alcohol toluene acetonitrile nitromethane n n dimethylformamide n n dimethylacetamide dimethylsulfoxide 3 methyl 1 butanol 2 methoxyethanol 2 propanol and xylene the addition conditions of step a further comprise a temperature of about 15 25 u00b0 c.