Use of DOE for rapid development of a red-Al reduction process for the synthesis of 3,4-isopropylidenedioxypyrrolidine hydrotosylate

Statistical design of experiments (DOE) was used to rapidly optimize Red-Al reduction of an imide to produce, after deprotection and salt formation, 3,4-isopropylidenedioxypyrrolidine hydrotosylate (1), an intermediate in the synthesis of Ingliforib. A Red-Al reduction process was successfully scaled to produce multikilogram quantities of 1, thus demonstrating a safer and more economical process. Further development resulted in an optimized procedure, which not only avoided borane reduction but also allowed the three-step procedure to be performed without isolation of the intermediates, solvent exchange, or distillation.