Cyclizations of γ-Hydroxyallenes Mediated by Organopalladium Halides: A Convergent Synthetic Route to Substituted 5-Alkenyl-2-furanones and 2-Alkenyltetrahydrofurans

Palladium-catalyzed approach to the synthesis of five-membered O-heterocycles

“…Walkup and Gallagher [36,37] reported a palladium-catalyzed 5-exo regioselective cyclization of allenes bearing a nucleophile in γ-position in the presence of iodobenzene. This kind of reactivity has marked a milestone in palladium catalyzed reaction of allenes; indeed, the authors proposed a mechanism that for the first time was not the one historically setup by Cazes and Tsuji [38][39][40] about intermolecular allenes Pd(0)-carbopalladation, that is, claiming for the formation of a allylic complex.…”

Heteroatom Nucleophile Induced C–C Fragmentations to Access Functionalized Allenes

“…Alternatively, such tetrasubstituted olefins are directly obtained from allenes 7 through a one-pot fragmentation-arylative cyclization sequence. [11] The addition of a catalytic amount of [Pd(dba) 2 ] and tricyclohexyl phosphine with phenyl iodide to allenes 7 induces lactonization to products 8e,f. From a mechanistic point of view, oxidative addition of Pd 0 to the aryl iodide generates an [Ar-Pd II -X] species which can act as a π-Lewis acid to activate the allene moiety of 5, thus promoting a Wacker-type cyclization followed by a reductive elimination.…”

“…A second possible mechanism is a carbo-palladation of the allene to form a π-allyl palladium intermediate which is trapped by an intramolecular nucleophilic attack of the carboxylic acid. [11] We then evaluated nitrogen-containing nucleophiles as a second major class of heteroatom nucleophiles for the fragmentation. We were pleased that they efficiently promote the reaction with only minor changes to the prior established reaction conditions.…”

Heteroatom‐Nucleophile‐Induced CC Fragmentations: Synthesis of Allenes and Entry to Domino Reactions

“…In the presence of catalytic amounts of [Pd(dba) 2 ] (dba = dibenzylideneacetone) and tricyclohexylphosphine, aryl iodides underwent arylative cyclization leading to 6 a-6 c ( Table 3, entries 6-8). [14] The reaction proceeded in good yields, though the stereoselectivity of the formed olefins was only modest when R 1 ¼ 6 R 2 (Table 3,…”