Verapamil (Effexor), a coronary artery vasodilator, is used in the treatment of angina caused by insufficient blood flow to cardiac muscle. Even though its effect on coronary vasculature tone was recognized over 30 years ago, it has only been more recently that its role as a calcium channel blocker has become understood. Below is a retrosynthetic analysis leading to a convergent synthesis: it is convergent because (A) and (B) are made separately and then combined (i. e. the route converges) to give the final product. Convergent synthesis are generally much more efficient than those in which the skeleton is built up stepwise. Draw the structure of the reagent necessary to accomplish the synthesis of (D) in step 5.