Continuous Flow Process for Reductive Deoxygenation of ω-Chloroketone in the Synthesis of Vilazodone

A continuous flow process for the reductive deoxygenation of 3-(4-chlorobutanoyl)-1H-indole-5-carbonitrile to 3-(4-chlorobutyl)-1H-indole-5-carbonitrile was developed using a continuous stirred tank reactor (CSTR) setup. The opportunity for process optimization as well as scale-up feasibility was investigated at a laboratory scale. Advantages of a continuous process such as increased product yield, minimized impurity formation, enhanced safety, and increased overall purity of the isolated material thereby avoiding a purification step were demonstrated. Both sodium borohydride and a borane·THF complex were explored as reducing agents in conjunction with iron trichloride which produced high purity 3-(4-chlorobutyl)-1H-indole-5-carbonitrile not requiring further purification in higher yield than the standard batch process.