Reaction SMILES: [BH-](OC(C)=O)(OC(C)=O)OC(C)=O.[Na+].CC(O)=O.[CH3:19][CH:20]1[CH2:24][CH2:23][CH2:22][NH:21]1.[CH:25]([C:27]1[S:31][C:30]([B:32]([OH:34])[OH:33])=[CH:29][CH:28]=1)=O>C([O-])(O)=O.[Na+].CO.C(Cl)Cl.CO>[CH3:19][CH:20]1[CH2:24][CH2:23][CH2:22][N:21]1[CH2:25][C:27]1[S:31][C:30]([B:32]([OH:34])[OH:33])=[CH:29][CH:28]=1
Reactant: CC1CCCN1
Reactant: O=Cc1ccc(B(O)O)s1
Agent: CC(=O)O[BH-](OC(C)=O)OC(C)=O
Agent: O=C([O-])O
Agent: [Na+]
Solvent: ClCCl
Solvent: CO
Solvent: CC(=O)O
Product: CC1CCCN1Cc1ccc(B(O)O)s1
Temperature: 25 °C
Reaction time: 15 h
Yield: 5.3 %

Procedure:
Batch 1: NaBH(OAc)3 (271 mg, 1.28 mmol), HOAc (0.07 mL), and 2-Methylpyrrolidine (0.043 mL, 0.42 mmol) were added to a solution of (5-formyl-2-thienyl)boronic acid (100 mg, 0.64 mmol) in CH2Cl2 (4 mL) in a 2-dram vial. The vial was capped and the reaction was stirred at room temperature for 15 h. The reaction mixture was loaded directly onto a 2 g SCX cartridge (pre-equilibrated with MeOH), eluting in sequence with MeOH (12 mL) and a 2 M solution of NH3/MeOH (8 mL). The fractions containing the boronic acid crude product were concentrated under a stream of N2 and dried under high vacuum to give 45 mg of crude product. The crude product was taken up in saturated NaHCO3 (2 mL) and extracted with EtOAc (3×2 mL) to give 6.6 mg of crude {5-[(2-methyl-1-pyrrolidinyl)methyl]-2-thienyl}boronic acid. Batch 2: NaBH(OAc)3 (271 mg, 1.28 mmol), HOAc (0.07 mL), and 2-Methylpyrrolidine (0.043 mL, 0.42 mmol) were added to a solution of (5-formyl-2-thienyl)boronic acid (100 mg, 0.64 mmol) in 1:1 CH2Cl2/MeOH (4 mL) in a 2-dram vial. The vial was capped and the reaction was stirred at room temperature for 15 h. The reaction mixture was loaded directly onto a 2 g SCX cartridge (pre-equilibrated with MeOH), eluting in sequence with MeOH (12 mL) and a 2 M solution of NH3/MeOH (8 mL). The fractions containing the boronic acid crude product were concentrated under a stream of N2 and dried under high vacuum to give 45 mg of crude product. The crude product was taken up in saturated NaHCO3 (2 mL) and extracted with EtOAc (3×2 mL) to give 5 mg of crude {5-[(2-methyl-1-pyrrolidinyl)methyl]-2-thienyl}boronic acid. Batch 3: 2-Methylpyrrolidine (0.033 mL, 0.32 mmol) was added to a solution of (5-formyl-2-thienyl)boronic acid (50 mg, 0.32 mmol) in MeOH (1 mL) in a 2-dram vial. The vial was capped and the reaction was stirred at room temperature for 2 h. NaCNBH3 (40 mg, 0.64 mol) was added, and stirring continued for 19 h. The reaction mixture was loaded directly onto a 2 g SCX cartridge (pre-equilibrated with MeOH), eluting in sequence with MeOH (12 mL) and a 2 M solution of NH3/MeOH (9 mL). The fractions containing the boronic acid crude product were concentrated under a stream of N2 and dried under high vacuum to give 45 mg of crude product. The crude product was taken up in saturated NaHCO3 (2 mL) and extracted with EtOAc (3×2 mL) to give 7.8 mg of crude {5-[(2-methyl-1-pyrrolidinyl)methyl]-2-thienyl}boronic acid. The crude boronic acid from the above three reactions were pooled and carried on for the preparation of 3-[1-(ethylsulfonyl)-4-piperidinyl]-5-{5-[(2-methyl-1-pyrrolidinyl)methyl]-2-thienyl}-1H-indole-7-carboxamide (final weight after pooling the three batches of {5-[(2-methyl-1-pyrrolidinyl)methyl]-2-thienyl}boronic acid was 19 mg).