Efficient synthesis of dichlorodenafil, an unapproved sildenafil analogue appearing in non-prescription supplements

We have developed an efficient synthesis of dichlorodenafil (4), an unapproved sildenafil analogue isolated from dietary supplements. Our sequence employs POCl₃-mediated chlorination of readily available chloroacetyl compound 7 followed by selective hydrolysis of the chloro-heterocycle function. Our synthesis confirms the structure of the illegal additive, and will provide regulatory agencies with ready access to authentic standard samples of dichlorodenafil (4) to aid in their mission to protect the public from unapproved and potentially harmful erectile dysfunction (ED) drug analogues that are added to herbal and dietary supplements without providing users with appropriate toxicological or pharmacological information.