Concise asymmetric synthesis of (−)-Bao Gong Teng A via Evans chiral auxiliary-based 1,3-dipolar cycloaddition†

We present a concise asymmetric synthesis of (−)-Bao Gong Teng A, a 2-hydroxylated tropane alkaloid with hypotensive and miotic activities isolated from the Chinese herb Erycibe obtusifolia Benth. Using an Evans chiral auxiliary, we achieve a regio- and stereoselective 1,3-dipolar cycloaddition between p-chlorobenzyl pyridinium salt and (R)-3-acryloyl-4-phenyloxazolidin-2-one, efficiently generating the tropane skeleton on a decagram scale. This methodology provides a rapid and practical synthesis of optically active (−)-Bao Gong Teng A for further biological studies.