Identification of the First Alkenyl Chiloglottone Congener

Abstract

Orchids of the genus Chiloglottis rely on sexual deception to attract a male thynnine wasp, whereupon a courtship routine results in the deposition and transfer of pollinia and subsequent pollination of the orchid. The chemical cues responsible for this behavior were recognized as a new class of natural products and efforts to synthetically prepare them, to assist in structural identification and to aid in ecological studies, have been ongoing. Most recently the first alkenylated member of this class was proposed based on GC–MS analysis of a physiologically active compound present in an orchid extract. The current work reveals synthetic efforts that provide access to diastereomerically pure unsaturated chiloglottone analogues and in combination with laboratory‐based electrophysiological assays and field‐based studies have unambiguously allowed identification of 5‐allyl‐2‐ethyl‐1,3‐cyclohexanedione (1d, chiloglottone 4) as the first alkenyl congener in the chiloglottone family. Convergent synthetic approaches, involving copper(I)‐mediated conjugate addition to a glutaconic ester converging on cadmium‐mediated desymmetrization of cyclic anhydrides or a Johnson–Claisen rearrangement of a mixed ketene acetal provided the appropriately substituted δ‐keto acids suitable for carbocyclization to furnish the required chiloglottone analogues.

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Enantioselective, Desymmetrizing, Bromolactonization Reactions of Symmetric Olefinic Dicarboxylic Acids

“…Our synthetic route to this substrate is shown in Scheme 4. Thus, the 1,4addition of b-ketoester 5 a to the known 1,5-diethyl 2-pentenedioate [15] afforded triester 6 a. Then, compound 6 a was subjected to Krapcho decarboxylation with NaCl in DMF and water, [16] followed by Wittig olefination with the ylide of CH 3 PPh 3 Br to produce olefinic diester 8 a. Hydrolysis of the diester groups in compound 8 a with LiOH gave dicarboxylic acid 3 a.…”

Annulations with Butenolides and Phthalides: New Entries to Isocoumarins, 3,4-Dihydroisocoumarins, and Benzofurans

“…In order to produce only the product from 1,4-addition, we generated epoxide 4 from methyl sorbate using the method of Barrow. 39 This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.…”