A method of making a compound of Formula I: wherein the content of the compounds of Formula Ia and Formula Ib: is less than 5% by weight, comprising: a) forming a first reaction mixture comprising a compound of Formula II: a non-nucleophilic base, a first solvent, and a compound of Formula IIIa: R 1a -LG 1a (IIIa), wherein the molar ratio of the compound of Formula IIIa to the compound of Formula II is greater than 1, and wherein the reaction mixture is mixed for at least two hours at or above room temperature under conditions suitable to form an intermediate mixture comprising the compound of Formula I and at least one compound of Formula Ia and Ib; a1) forming a second reaction mixture comprising the intermediate mixture, and a compound of Formula IIIb: R 1b -LG 1b (IIIb), wherein the molar ratio of the compound of Formula IIIb to the compounds of the intermediate mixture is greater than 1, and wherein the second reaction mixture is mixed for at least two hours at or above room temperature under conditions suitable to form at least one compound of Formula IVa or Formula IVb: b) forming a partition mixture comprising the second reaction mixture, water and an organic solvent to form an aqueous layer and an organic layer; and c) separating the organic layer and aqueous layer to isolate the compound of Formula I, wherein the content of the compounds of Formula Ia, Formula Ib, Formula IVa and Formula IVb is less than 5% by weight, wherein R 1a and R 1b are independently methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, iso-butyl or cyclopropylmethyl, such that R 1b is different than R 1a; R 2 is halogen, SCH 2 Ar or SCHAr 2, wherein each Ar is phenyl optionally substituted with 1-3 R 2a groups each independently halogen, C 1 -C 6 alkyl, C 1 -C 6 haloalkyl, C 1 -C 6 alkoxy, or C 1 -C 6 haloalkoxy; LG 1a is Br, I or OSO 2 R 3; LG 1b is OSO 2 R 3; and R 3 is C 1 -C 6 alkyl, C 1 -C 6 haloalkyl, or C 6 -C 12 aryl, wherein the aryl group is substituted with 1-3 R 3a groups each independently hydrogen, C 1 -C 6 alkyl, halogen, or NO 2. wherein the content of the compounds of Formula Ia and Formula Ib: is less than 5% by weight, a) forming a first reaction mixture comprising a compound of Formula II: a non-nucleophilic base, a first solvent, and a compound of Formula IIIa: R 1a -LG 1a (IIIa), wherein the molar ratio of the compound of Formula IIIa to the compound of Formula II is greater than 1, and wherein the reaction mixture is mixed for at least two hours at or above room temperature under conditions suitable to form an intermediate mixture comprising the compound of Formula I and at least one compound of Formula Ia and Ib; a non-nucleophilic base, a first solvent, and a compound of Formula IIIa: R 1a -LG 1a (IIIa), wherein the molar ratio of the compound of Formula IIIa to the compound of Formula II is greater than 1, and wherein the reaction mixture is mixed for at least two hours at or above room temperature under conditions suitable to form an intermediate mixture comprising the compound of Formula I and at least one compound of Formula Ia and Ib; a1) forming a second reaction mixture comprising the intermediate mixture, and a compound of Formula IIIb: R 1b -LG 1b (IIIb), wherein the molar ratio of the compound of Formula IIIb to the compounds of the intermediate mixture is greater than 1, and wherein the second reaction mixture is mixed for at least two hours at or above room temperature under conditions suitable to form at least one compound of Formula IVa or Formula IVb: b) forming a partition mixture comprising the second reaction mixture, water and an organic solvent to form an aqueous layer and an organic layer; and c) separating the organic layer and aqueous layer to isolate the compound of Formula I, wherein the content of the compounds of Formula Ia, Formula Ib, Formula IVa and Formula IVb is less than 5% by weight, R 1a and R 1b are independently methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, iso-butyl or cyclopropylmethyl, such that R 1b is different than R 1a; R 2 is halogen, SCH 2 Ar or SCHAr 2, wherein each Ar is phenyl optionally substituted with 1-3 R 2a groups each independently halogen, C 1 -C 6 alkyl, C 1 -C 6 haloalkyl, C 1 -C 6 alkoxy, or C 1 -C 6 haloalkoxy; LG 1a is Br, I or OSO 2 R 3; LG 1b is OSO 2 R 3; and R 3 is C 1 -C 6 alkyl, C 1 -C 6 haloalkyl, or C 6 -C 12 aryl, wherein the aryl group is substituted with 1-3 R 3a groups each independently hydrogen, C 1 -C 6 alkyl, halogen, or NO 2.