Synthesizing Allenes Today (1982-2006)

Abstract

Allenes have allowed chemists to access a variety of structurally interesting and biologically active products. The emergence of these unique compounds in organic synthesis is a direct result of the discovery and development of efficient protocols for their preparation. Moreover, efficient syntheses of the allenyl functionality are important to the synthetic community and will be reported and discussed in this review.

Allene formation by gold catalyzed cross-coupling of masked carbenes and vinylidenes

“…4), respectively. Most of the stoichiometric processes can be extended to the preparation of allenes (15)(16)(17) by analogous ''carbene/vinylidene cross-coupling'' processes ( Fig. 1, Eq.…”

“…In the last decade, allenes have evolved from exotic molecules into extremely useful synthons in natural-product construction (15,16). Considering the lack of efficient and versatile catalytic processes to assemble directly the skeletal carbons of the allene -system from two different fragments, a general coupling protocol is highly desirable.…”

Palladium(0)‐Catalyzed Cross‐Coupling of 1,1‐Diboronates with Vinyl Bromides and 1,1‐Dibromoalkenes

“…[7,8] Under the reaction conditions shown in Equation (1), the substrate scope was next investigated. First, various dibromoalkenes [c] 14 R = Me, 1 l 2 a 4 n, 94 2:1 15 [d] R = cyclohexyl, 1 m 2 a 4 o, 84 2:1 [c] [a] Reaction conditions: 1 (1.0 mmol), 2 (0.75 mmol), [Pd(PtBu 3 ) 2 ] (5 mol %), LiOH (4 m, 625 mL), 1,4-dioxane (5 mL).…”

Durch Heteroatom‐Nukleophile induzierte C‐C‐Fragmentierungen: Synthese von Allenen und Ausgangspunkt für Dominoreaktionen

“…[4] Der zunehmende präparative Nutzen der Allene führt dazu, dass neue Herstellungsmethoden immer mehr in der Vordergrund rücken. [5] Durch die wegweisenden Arbeiten von Eschenmoser [6] und die darauffolgenden Studien von Grob [7] haben C-CBindungsspaltungen, die gleichzeitig zu Carbonylgruppen und Doppelbindungen führen, vielfältige Anwendungen in der Synthese gefunden. [8] Dudley und Mitarbeiter entwickelten durch Nukleophile induzierte Grob-Fragmentierungen von vinylogen Acyltriflaten, die w-Carbonyl-funktionalisierte Alkine ergeben.…”