Dicyclohexylamine → (r)-2-Bromoisovaleric acid dicyclohexylamine salt

To 11.81 g of a toluene solution of (R)-2-bromoisovaleric acid obtained in Example 1 (containing 3.00 g of (R)-2-bromoisovaleric acid), 3.19 g of toluene was further added. After continuously adding 3.00 g of dicyclohexylamine under a nitrogen atmosphere at 5° C. for 1 hour to crystallize. They were successively stirred at 5° C. for 2 hours. The obtained crystals were filtered under a reduced pressure and then the crystals were washed with 3 ml of toluene. The obtained crystals were dried under a reduced pressure to obtain 4.84 g of a (R)-2-bromoisovaleric acid dicyclohexylamine salt (optical purity 99.4% ee, crystallization yield 81%, apparent purity 94.5%, impurity content 2-hydroxy isovaleric acid: 0.04%, bromine content: 3.02%).