Dipolar cycloaddition route to diverse analogues of cocaine: The 6- and 7-substituted 3-phenyltropanes

In our quest for an antagonist or partial agonist of cocaine, access to certain 6- and 7-substituted 3-phenyltropanes of type I was required. Starting from 3-hydroxy-1-methyl-4-phenylpyridinium iodide, we disclose a pyridinium betaine-based dipolar cycloaddition route to tropenones of type II. In turn, we show how this intermediate can be transformed to type I products either through the copper-catalyzed conjugate addition reaction of Grignard reagents to the enones 7-9 or by the copper(I)-catalyzed cross coupling reaction of the allylic acetates 15a and 16a with Grignard reagents.