the following describes the present invention in more detail with reference to examples . the symbols and abbreviations used in the examples are as they are usually used in the chemical field , unless otherwise stated . khf 2 ( 5 . 17 g , 66 mmol ) and ch 2 cl 2 ( 30 ml ) were placed in a teflon ( registered trademark ) container , and cooled to − 78 ° c ., followed by dropwise addition of brf 3 ( 4 . 54 g , 33 mmol ). while the temperature was maintained , the mixture was stirred for 30 minutes , and the temperature was increased to room temperature . the liquid portion was removed , and the solid portion was washed by adding 20 ml of ch 2 cl 2 , the procedure of which was repeated three times . the resulting product was then stirred while nitrogen was blown in to obtain a complex ( brf 3 - 2khf 2 complex ) ( 8 . 84 g , 91 %) as a solid by reacting 2 mol of khf 2 , per mol of brf 3 . the obtained complex was mixed with methylene chloride at room temperature ; however , an exothermic phenomenon was not observed , and no reaction occurred . the exothermic decomposition onset temperature in nitrogen of the complex was measured by the method described above and was 197 ° c . kf ( 2 . 5 g , 44 mmol ) and ch 2 cl 2 ( 10 ml ) were placed in a teflon ( registered trademark ) container and cooled to − 78 ° c ., followed by dropwise addition of brf 3 ( 3 . 0 g , 22 mmol ). while the temperature was maintained , the mixture was stirred for 30 minutes , and the temperature was increased to room temperature . the liquid portion was removed , and the solid portion was washed by adding 5 ml of ch 2 cl 2 , the procedure of which was repeated three times . the resulting product was then stirred while nitrogen was blown in to obtain a complex ( brf 3 - 2kf complex ) as a solid by reacting 2 mol of kf , per mol of brf 3 . the obtained complex was mixed with methylene chloride at room temperature ; however , an exothermic phenomenon was not observed , and no reaction occurred . the exothermic decomposition onset temperature in nitrogen of the complex was measured by the method described above and was 252 ° c . the brf 3 - 2khf 2 complex ( 193 mg , 0 . 66 mmol ) obtained in example 1 and ch 2 cl 2 ( 2 . 4 ml ) were placed in a teflon ( registered trademark ) container . then , compound 1a ( 100 mg , 0 . 3 mmol ) shown in table 1 below was added thereto at room temperature and stirred for 1 hour while the temperature was maintained . after the completion of the reaction , the resulting product was quenched with the addition of water , and after separation , the washing was performed with a saturated aqueous nahco 3 solution and a saturated aqueous na 2 s 2 o 3 solution . the organic layer was dried over mgso 4 and concentrated , followed by purification by silica column chromatography . in this manner , compound 2a ( 57 mg , 84 %) shown in table 1 below was obtained . the desulfurization - difluorination reaction was performed as in example 3 , except that compounds 1b to 1d shown in table 1 below were used as the starting material in place of compound 1a used in example 3 , and that the molar ratio of the fluorinating agent to the starting material and the reaction time were changed to the values shown in table 1 . table 1 shows the resulting products and their yields . in each table below , the values shown in the “ yield ” columns are isolated yields , and the values in parentheses are yields calculated from f - nmr . the desulfurization - difluorination reaction was performed as in example 3 , except that compound 1e shown in table 2 below was used as the starting material in place of compound 1a used in example 3 , and that the molar ratio of the fluorinating agent to the starting material and the reaction time were changed to the values shown in table 2 . table 2 shows the resulting product and the yield . the desulfurization - fluorination reaction was performed as in example 3 , except that compound 1f or 1g shown in table 3 below was used as the starting material in place of compound 1a used in example 3 , and that the molar ratio of the fluorinating agent to the starting material , the reaction temperature , and the reaction time were changed to the values shown in table 3 . table 3 shows the resulting products and their yields . the desulfurization - fluorination reaction was performed as in example 3 , except that compound 1h or 1i shown in table 4 below was used as the starting material in place of compound 1a used in example 3 , and that the molar ratio of the fluorinating agent to the starting material and the reaction time were changed to the values shown in table 4 . table 4 shows the resulting products and their yields . the desulfurization fluorination reaction was performed as in example 3 , except that compound 1j shown in table 5 below was used as the starting material in place of compound 1a used in example 3 , and that the molar ratio of the fluorinating agent to the starting material and the reaction time were changed to the values shown in table 5 . the resulting product and the yield are shown in table 5 . the yield of the α - form was 52 % while the yield of the β - form was 31 %, and the total yield of both was 83 %. the desulfurization fluorination reaction was performed as in example 3 , except that compound 1j - 2 shown in table 5 below was used as the starting material in place of compound 1a used in example 3 , and that the molar ratio of the fluorinating agent to the starting material and the reaction time were changed to the values shown in table 5 . the resulting product and the yield are shown in table 5 . the yield of the α - form was 52 % while the yield of the β - form was 31 %, and total yield of both was 83 %. the desulfurization - fluorination reaction was performed as in example 3 , except that compound 1k shown in table 6 below was used as the starting material in place of compound 1a used in example 3 , and that the molar ratio of the fluorinating agent to the starting material and the reaction time were changed to the values shown in table 6 . table 6 shows the resulting product and the yield . the brf 3 - 2 ( khf 2 ) complex ( 293 mg , 1 mmol ) obtained in example 1 and ch 2 cl 2 ( 5 ml ) were placed in a teflon ( registered trademark ) container . then , compound 11 ( 68 mg , 0 . 5 mmol ) shown in table 7 below was added thereto at − 40 ° c . and stirred for 24 hour while the temperature was maintained . after the completion of the reaction , the resulting product was quenched with the addition of water , and after separation , the washing was performed with a saturated aqueous nahco 3 solution and a saturated aqueous na 2 s 2 o 3 solution . the organic layer was dried over mgso 4 and concentrated , followed by purification by silica column chromatography . in this manner , compound 2l ( 58 mg , 50 %) was obtained . the desulfurization - difluorination reaction was performed as in example 3 , except that compound 1m shown in table 8 below was used as the starting material in place of compound 1a used in example 3 , and that the molar ratio of the fluorinating agent to the starting material and the reaction time were changed to the values shown in table 8 . table 8 shows the resulting product and the yield . the desulfurization fluorination reaction was performed as in example 3 , except that compounds 1o to 1q shown in table 9 below were used as the starting material in place of compound 1a used in example 3 , and that the molar ratio of the fluorinating agent to the starting material , the reaction temperature , and the reaction time were changed to the values shown in table 9 . table 9 shows the resulting products and their yields . the desulfurization - fluorination reaction was performed as in example 3 , except that compounds 1r to 1t shown in table 10 below were used as the starting material in place of compound 1a used in example 3 , and that the molar ratio of the fluorinating agent to the starting material , the reaction temperature , and the reaction time were changed to the values shown in table 10 . table 10 shows the resulting products and their yields . the desulfurization fluorination reaction was performed as in example 3 , except that compound 1u shown in table 11 below was used as the starting material in place of compound 1a used in example 3 , and that the molar ratio of the fluorinating agent to the starting material , the reaction temperature , and the reaction time were changed to the values shown in table 11 . table 11 shows the resulting product and the yield .