O=P12OP3(OP(OP(O3)(O1)=O)(=O)O2)=O.CS(O)(=O)=O.[CH3:20][O:21][C:22]1[CH:23]=[C:24]([CH2:28][CH2:29][C:30]2[CH:38]=[CH:37][CH:36]=[CH:35][C:31]=2[C:32]([OH:34])=O)[CH:25]=[CH:26][CH:27]=1>>[CH3:20][O:21][C:22]1[CH:27]=[CH:26][C:25]2[C:32](=[O:34])[C:31]3[CH:35]=[CH:36][CH:37]=[CH:38][C:30]=3[CH2:29][CH2:28][C:24]=2[CH:23]=1To 5 g of phosphorous pentoxide was added 50 ml of methane sulphonic acid. The mixture was heated to 80° C. for 1 hour. The reaction mixture was brought down to 40° C. and 3 g (11.7 mmol) of 2 was added as solid. The mixture was heated at 40° C. for 1 hour and cooled down to room temperature. The reaction mixture was poured into 300 ml of ice/water and extracted with 200 ml of ethyl acetate. The organic layer was washed with 2×150 ml of water, 2×150 ml of saturated NaHCO3 and 100 ml of water. The resulting organic layer was dried (Na2SO4) and concentrated to give 2.6 g (11.7 mmol, 94%) of 3 as off-white powder.
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