Dipolar Cycloaddition Route to Diverse Analogues of Cocaine: The 6- and 7-Substituted 3-Phenyltropanes

Abstract
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.

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