[CH:1]12[CH2:10][C:5]3(O)[CH2:6][CH:7]([CH2:9][CH:3]([CH2:4]3)[NH:2]1)[CH2:8]2.[CH:12]([OH:14])=[O:13].OS(O)(=O)=O.O=S(=O)=O.[CH3:24]O>>[CH:1]12[CH2:10][C:5]3([C:12]([O:14][CH3:24])=[O:13])[CH2:6][CH:7]([CH2:9][CH:3]([CH2:4]3)[NH:2]1)[CH2:8]2To 2-azatricyclo[3.3.1.13,7]decan-5-ol (Intermediate-7) (1.5 g, 5.9 mmol, 1 eq), 98% formic acid (9 ml) was added drop wise with vigorous gas evolution for over 30 minutes to a rapidly stirred 30% oleum (36 ml) heated to 60° C. Upon completion of this addition, 99% formic acid (9 ml) was slowly added for the next 30 minutes. The reaction mixture was stirred for another 1 hr at 60° C. (monitored by LCMS). The reaction mixture thus formed was then slowly poured into vigorously stirred methanol (75 ml) cooled to 00° C. The mixture was allowed to slowly warm to room temperature while stirring the reaction mixture for 4-5 hrs. The mixture was then concentrated under vacuum. The residue was poured into ice (30 g) and basified with saturated Na2CO3 solution. The aqueous layer was extracted with 5% methanol in DCM (3×100 ml). Combined organic layer was washed with brine and dried over Na2SO4. The organic layer was finally concentrated to get intermediate-8, (550 mg, 50% yield) as an oily mass.
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