CuI-Catalyzed [3+2] Cycloaddition of Hindered Vinylidenebisphosphonates (VBP) with Azomethine Imines for Highly Regioselective Access to Dinitrogen-Heterobicycle-Containing Bisphosphonates

A concise, atom-economic, and highly regioselective synthetic strategy for the construction of several dinitrogen-fused heterocycles bearing bisphosphonates by 1,3-dipolar cycloaddition reaction of azomethine imines with tetraethyl vinylidene-1,1-bisphosphonate in the presence of CuI in toluene media has been developed. The targeted compounds were obtained in good yields and with excellent regioselectivity. This method for the synthesis of gem-bisphosphonates (BPs) is particularly attractive due to features such as low cost, mild conditions, atom economy, high stereoselectivity, and potential biological activity of the product.