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Pyranophane Transannular Diels−Alder Approach to (+)-Chatancin:  A Biomimetic Asymmetric Total Synthesis

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posted on 26.12.2003, 00:00 by Pierre Soucy, Alexandre L'Heureux, András Toró, Pierre Deslongchamps
An asymmetric total synthesis of (+)-chatancin was achieved via a transannular Diels−Alder (TADA) reaction of an in situ generated macrocyclic pyranophane pseudobase. The presented route constitutes the second of two proposed biosynthetic pathways that involves a TADA reaction. It links this diterpene biogenetically to the cembranoids. A set of TADA selection rules that rationalize the formation of (+)-chatancin from a dynamic equilibrium of four 2-hydroxy-2H-pyrane bicycles and their 16 potential TADA transition states are also outlined. Beyond the TADA reaction, highlights of the synthetic work include the assembly of a chiral acyclic macrocyclization substrate from (S)-citronellol and an efficient macrocyclization via a β-ketosulfoxyde/enone Michael addition.