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Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
Michael cyclization of both stereoisomers of Passerini products 20a and 20b. * means both R and S diastereoisomers of 20a or 20b, which have been independently converted into 24/25 (anti-20a or anti-20b) and 26/27 (syn-20a or syn-20b).