Development of a Practical Process for the Synthesis of PDE4 Inhibitors

A practical, safe, and efficient process for the synthesis of PDE4 (phosphodiesterase type 4) inhibitors represented by 1 and 2 was developed and demonstrated on a multi-kilogram scale. Key aspects of the process include the regioselective synthesis of dihydrothieno[3,2-d]pyrimidine-2,4-diol 9 and the asymmetric sulfur oxidation of intermediate 11.