Norbadione A: Synthetic Approach to the Bis(pulvinic acid) Moiety and Cesium‐Complexation Studies

Abstract

Das permethylierte Analogon 1 des Pilzinhaltsstoffs Norbadion A wurde durch zweifache Suzuki‐Miyaura‐Kupplung des Naphthalindiboronsäureesters 2 mit dem Triflat 3 erhalten. ESI‐MS‐Untersuchungen zufolge sind die Komplexe des Dikaliumsalzes von Norbadion A und von 1 mit Caesium ähnlich stabil, d. h., die Caesium‐Komplexierung erfolgt sehr wahrscheinlich über die Pulvinsäure‐Einheiten beider Verbindungen.

Synthesis of Leprapinic Acid, Calycine and Analogues by Sequential “[3+2] Cyclization/Suzuki/Lactonization” Reactions

“…Treatment of 8b with BBr 3 afforded the calycine analogue E-9b (38 %). The configuration of the butenolide was established in analogy to related reactions [10][11][12] and based on the known structure of calycine. As mentioned above, treatment of the butenolide 8a with four equivalents of BBr 3 resulted in cleavage of both methyl ether groups to give calycine.…”

“…The reaction of (o-hydroxyphenyl)acetic acid with acetic anhydride afforded, following a known procedure, [14] 3-acetylbenzofuran-2-one (12), which resides exclusively in its enolic form (Scheme 4). The reaction of the dianion of 12 with N,NЈ-dimethoxy-N,NЈ-(dimethyl)ethanediamide (13) [15] afforded, as we have reported earlier,…”

“…[7] We and others have reported the functionalization of γ-alkylidene-α-hydroxybutenolides, readily available by cyclization of 1,3-bis(silyl enol ether)s [8,9] with oxalyl chloride, [10] by Stille and Suzuki cross-coupling reactions. [11][12][13] The application of the Suzuki reaction allowed a convenient synthesis of pulvinic acids [11] and of an analogue of the natural product norbadione A.[12] Herein, we wish to report the application of our methodology to the synthesis of calycine and analogues. In addition, a new and convenient synthesis of leprapinic acid by chemoselective deprotection of per- methylated leprapinic acid is reported.…”

“…[11][12][13] The application of the Suzuki reaction allowed a convenient synthesis of pulvinic acids [11] and of an analogue of the natural product norbadione A. [12] Herein, we wish to report the application of our methodology to the synthesis of calycine and analogues. In addition, a new and convenient synthesis of leprapinic acid by chemoselective deprotection of per-methylated leprapinic acid is reported.…”

Defunctionalization of γ‐Alkylidene‐α‐hydroxybutenolides by Palladium(0)‐Catalyzed Reaction of Enol Triflates with Hexylboronic Acid

“…This approach has been successfully applied to the synthesis of a number of natural products, such as pulvinic acids [8] or linderone and lucidone; [9] in addition, an analog of norbadione A has been recently prepared. [10] During a synthetic project, there was the need to replace the α-hydroxy group of the butenolide by a hydrogen atom. Brückner et al reported Stille reactions of butenolide-derived enol triflates with Bu 3 SnH using catalytic amounts of palladium catalysts or NiCl 2 (PPh 3 ) 2 .…”