Eine neue Strategie für die Synthese des Butenolid‐Teils von Peridinin

Abstract

Weinsäure diente als Startverbindung für die stereoselektive Synthese des Butenolid‐Teils (siehe Bild) von Peridinin, einem marinen Carotinoid. Schlüsselschritte waren die Desymmetrisierung des doppelten Weinrebamids der Weinsäure, die ungewöhnliche Reduktion eines weiteren Weinrebamids, eine E‐selektive Olefinierung mit Bromphosphonaten vom Ando‐Typ und eine anti‐selektive Mitsunobu‐Eliminierung (zur Einführung der C1′Cγ‐Bindung).

Total Synthesis of the Light‐Harvesting Carotenoid Peridinin

“…[13,14] Entities like the 3-alkenyl-5-(ahydroxyalkyl)butenolide exhibiting the required ul relationship [15] between their stereocenters can be obtained by appropriate modification of the termini of diethyl tartrate (6). We showed this in a model study [16] and chose to exploit it here. Compound 4 was endowed with an oxo function in order to take up allenylsulfone 2 in a (Sylvestre) Julia olefination and with a bromoolefin moiety for a Stille coupling with alkenylstannane 3.…”

“…[17] Compound 5 is a common starting material for the synthesis of 4''-hydroxylated [18] carotenoids like zeaxanthin [19] and peridinin. [10][11][12] Starting from (+)-diethyl tartrate (6), the ester-containing Weinreb amide 7 was prepared in four steps and 58 % overall yield as described earlier [16] (Scheme 2). The selective reduction both of the ester (!CH 2 OH) and amide (!CHO) moieties succeeded only when a distinct excess of NaAlH 4 was used.…”

“…Surprisingly the ensuing anti elimination 11!12 failed under established [16] Mitsunobu conditions (PPh 3 , diethyl azodicarboxylate, THF, À30 8C; Scheme 2). This was also true for related 5-(a-hydroxyalkyl)butenolides, for example, the coupling product obtained from 11 and 3, and the diol obtained from 10 by deprotection/lactonization.…”

Total Synthesis of Naturally Configured Pyrrhoxanthin, a Carotenoid Butenolide from Plankton

“…This was possible by addition of thiocarbonyldiimidazole in analogy to the procedure described recently for an analogous dehydration. [17] However, the reaction got stuck after the initial O functionalization had occurred. In contrast to the preceding case [17] the anti elimination followed only after the addition of triethylamine-but then within a few seconds.…”

“…[17] However, the reaction got stuck after the initial O functionalization had occurred. In contrast to the preceding case [17] the anti elimination followed only after the addition of triethylamine-but then within a few seconds. A 91:9 Z/E mixture of the alkylidenebutenolides formed, from which we isolated the Z isomer 33 by flash chromatography on silica gel [35] in 73 % yield.…”