Advances in the stereoselective synthesis of antifungal agents and ...

Chapter 8 168and the stirring was continued for about 24 h. The solvent was removedby evaporation on a rotavapor, the crude oil dissolved in CH 2 Cl 2, filteredthrough a Florosil pad and then purified by flash chromatography(CH 2 Cl 2 ) on silica gel.See chapter 4 and table 4.6 for chemical yields and enantiomericeccesses.8.20.2 General azide synthesis by diazabicycloundecene(DBU) and diphenylphosphorylazide (DPPA):Alcohol 27 (1 mmol) and DPPA (1.2 mmol) were dissolved in drytoluene so that the final concentration of the alcohol was ca. 0.5-1 M. Tothe mixture was added a slight excess of DBU (1.1-1.5 mmol). Thereaction mixture was stirred 12-24 h at RT, was then diluted with tolueneand washed consecutively with 1 N HCl, saturated NaCl solution and driedover anhydrous Na 2 SO 4 . After solvent evaporation the crude oil waspurified by flash chromatography (CH 2 Cl 2 ) on silica gel .See chapter 4, table 4.7 for chemical yields and enantiomericpurities.8.21 General procedures for the synthesis of amines 56a-d:8.21.1 Reduction of azides 55 by Ph 3 P/H 2 O:To a solution of azide 55 (1 mmol) in THF/water 10:1 a solution ofPh 3 P in THF was added. The mixture was stirred for 3 h. The solvent wasevaporated and the crude oil was purified by flash chromatography oversilica gel.See chapter 4, table 4.8, method A for the chemical yields.8.21.2 Reduction of Azides 55 by SnCl 2 :To a stirred suspension of stannous chloride (2mmol) in methanol, asolution of azide 55 (1mmol) in methanol was added dropwise. Thereaction was exothermic and N 2 gas evolved. The mixture was stirred at