24  US 8,283,102  B2  23  yield: 68%) of a bicyclo[2.2.1 ]heptane-2-carboxylic acid-2,  2-difluoro-2-sulfo-ethy 1 ester dipheny 1-4-acroy loxy-pheny 1- sulfonium salt, and a structure of the bicyclo[2.2.l]heptane- 2-carboxylic acid-2,2-difluoro-2-sulfo-ethyl ester diphenyl- 4-acroyloxy-phenylsulfonium  salt  was  observed  $^{1}$H-NMR:  $^{1}$H-NMR (chloroform-d3, reference: tetramethylsilane):  (ppm) 1.21-2.79 (m, 14H), 4.54 (m, 2H), 6.21 (d, lH), 6.39 (t,  lH), 6.87 (d, lH) 7.45 (d, 2H), 7.65-7.76 (m, !OH), 7.86 (d,  2H),  difluoro-2-sulfo-ethyl  ester  diphenyl-4- hydroxyphenylsulfonium salt was observed by $^{1 }$H-NMR (see  FIG.  6):  $^{1}$H-NMR (chloroform-d3, reference: tetramethylsilane):  (ppm) 0.83 (t, 3H), 1.32 (m, 6H), 1.61 (m, 2H), 1.38 (t, 2H),  4.78 (t, 2H), 7.05 (d, 2H), 7.35 (d, 2H), 7.55-7.78 (m, !OH),  About 8.87 g of the heptanoic acid-2,2-difluoro-2-sulfo› ethyl ester diphenyl-4-hydroxyphenylsulfonium salt manu› factured in the synthesis example 7, about 1.5 ml of meth› acryloyl chloride, and about 17.4 mg of 4-methoxyphenol  (MEHQ) were mixed and stirred in about 150 ml of an MC,  about 3.71 ml of diisopropylethylamine (DIPEA) was gradu› ally dropped using a dropping funnel under an ice bath, and a  synthesis reaction (see Equation 8 below) was performed  while stirring for about three hours at room temperature. In  this instance, 4-dimethylaminopyridine (DMAP) was used as  a reaction catalyst, and a process of the synthesis reaction was  observed by $^{19}$F NMR using a small amount of an extracted  organic phase. The organic phase was extracted when the  synthesis reaction was terminated, and washed using IN HCl,  distilled water, a saturated sodium bicarbonate aqueous solu› tion, and distilled water in the stated order (three times). Next,  a solvent was removed, and washing with the MC of a soluble  solvent and hexane of a sparingly soluble solvent was per› formed.  Next, the solvents were removed, and drying under a  reduced pressure was performed to obtain about 8.46 g (a  yield: 97 .2%) of a heptanoic acid-2,2-difluoro-2-sulfo-ethyl  About 7 g of the diphenyl-4-hydroxyphenylsulfonium tri› fluoromethanesulfonate salt and about 5.81 g of a heptanoic  acid-2,2-difluoro-2-sulfo-ethyl ester sodium salt were dis› solved in about 100 ml of an MC and about 100 ml of water,  and a synthesis reaction (see Equation 7 below) was per› formed while strongly stirring for three hours. In this  instance, a process of the synthesis reaction was observed by  $^{19}$F NMR using a small amount of an extracted organic phase.  The organic phase was extracted when the synthesis reac› tion was terminated, and a solvent was removed. Next, wash› ing with the MC of a soluble solvent and hexane of a sparingly  soluble solvent was performed. Next, the solvents were  removed, and drying under a reduced pressure was performed  to obtain about 8.87 g (a yield: 98.5%) of a heptanoic acid- 2,2-difluoro-2-sulfo-ethyl ester diphenyl-4-hydroxyphenyl› sulfonium salt, and a structure of the heptanoic acid-2,2- Heptanoic acid-2,2-difluoro-2-sulfo-ethyl Ester  Dipheny 1-4-methacroy loxy-pheny lsulfonium Salt  Synthesis  Synthesis Example 8  Synthesis Example 7  Heptanoic acid-2,2-difluoro-2-sulfo-ethyl Ester  Diphenyl-4-hydroxyphenylsulfonium Salt Synthesis  Qo  O-¢s+_o-~-CF3  ~  0  ~I  OH  0  0  II  ~  MC/DW  Na+_ O,.., .. t,,C ../’-._O  o  F2  s  Q"  0  ~I  ~  OH  Q"  0  ~  I  ~  OH  - O  1) DIPEA, 2) DMAP  3)MEHQ  [Equation 7]  [Equation 6] 