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

Stereocomplementary Syntheses of 1,ω‐DistannylatedE,Z‐Isomeric Conjugated Trienes, Tetraenes, and Pentaenes

“…By applying a protocol to make tin‐free conjugated trienes in one‐pot sulfone bromination/Ramberg–Bäcklund reactions,24 we treated the distannylated diallylsulfone 8 9 (Scheme ) and the similar compounds 11 , 14 , and 17 (Schemes 4–, respectively) with CBr 2 F 2 and KOH on Al 2 O 3 25 between 0 °C and room temperature. Purification by flash chromatography on silica gel26 provided the distannylated trienes 9 9 (80–82 %), 12 (55 %), 15 (80–82 %), and 18 (75–77 % yield; Schemes 3–, respectively). These compounds were obtained as 87:13–100:0 mixtures of the all‐ E and mono‐ Z isomers.…”

“…The convergency of Stille coupling strategies increases when three components are involved and one is a 1,2‐distannylated ethene, 1,4‐distannylated buta‐1,3‐diene, or 1,ω‐distannylated linear conjugated polyene. In spite of this conceptional advantage, such tandem Stille couplings have been reported only occasionally, that is, for E ‐1,2‐bis(tributylstannyl)ethene a few times,3, 4 an isomeric mixture of 1,4‐bis(trimethylstannyl)buta‐1,3‐dienes in two studies,5 1,6‐bis(tributylstannyl)hexa‐1,3,5‐triene (all‐ E ‐ 2 ; Scheme ) as an intermediate for syntheses of xerulinic acid6–8 and xerulin,8 1,6‐bis(tributylstannyl)hepta‐1,3,5‐triene (all‐ E ‐ 9 ; see Scheme ) as an intermediate for pyrrhoxanthin,9 and 1,10‐bis(tributylstannyl)‐1,3,5,7,9‐decapentaene (mono‐ Z ‐ 32 ; see Scheme ) as an intermediate for β‐carotene 10. The respective distannanes in the cited examples linked two different electrophiles either intramolecularly3 or intermolecularly4f, 5a, 6–9 or two equivalents of a single electrophile 4a.…”

Sequential Hiyama Coupling/Narasaka Acylation Reaction of (E)‐1,2‐Disilylethene: Rapid Assembly of α,β‐Unsaturated Carbonyl Motifs

“…The reason for the observed chemoselectivity was that selective fluoride-based activation of the diethoxy(methyl)silyl moiety occurred to effect transmetallation. The corresponding homogeneous catalyst, Pd(OAc) 2 , also provided the desired products 10 and 11, but in slightly lower yields (62 and 86 %, respectively). acid anhydrides.…”

“…Its polyunsaturated nature made the synthesis particularly challenging due to its sensitivity to light, oxygen, Rapid Assembly of α,β-Unsaturated Carbonyl Motifs Table 1. Access to stereodefined and conjugated α,β-unsaturated ketones 12a-p. [a,b] [a] Method A: 1) 5 (0.50 mmol), R 1 I (0.39 mmol), 14 (0.54 mmol), 9 (9.0 mol-% Pd), dioxane (2 mL), 60°C for 2 h; 2) (R 2 CO) 2 and many common synthetic reagents. This material has been recently utilized in the Julià-Colonna asymmetric procedure to furnish a valuable optically active epoxide.…”

“…As an elegant demonstration of this assembly strategy, Burghart and Bruckner very recently used a heptatrienyldistannane building block 2 in the total synthesis of the naturally configured pyrrhoxanthin (marine carotenoid product) by iterative Stille coupling reactions ( Figure 1). [2] The design of differentially functionalized building blocks and the development of reaction sequences that allow other key structural units are of intense ongoing synthetic interest. In contrast to olefin templates, very few examples of molecules that give access to α,β-unsaturated carbonyl motifs have been reported in the literature, despite their key role in organic synthesis.…”