Intramolecular Palladium(II)-Catalyzed 1,2-Addition to Allenes

Abstract

Palladium(II)-catalyzed intramolecular 1,2-additions to allenes substituted with an internal nucleophile have been developed. Carboxylic acids, alcohols, N-substituted amides, and carbamates were used as internal nucleophiles in the palladium-catalyzed reaction, which afforded lactones, tetrahydropyrans, tetrahydrofurans, pyrrolidines, and oxazolidinones in good isolated yields. The reactions were performed in the presence of LiBr with Pd(OAc) 2 as the catalyst. Two different reoxidants, p-benzoquinone or Cu(OAc) 2 , were used, the choice of oxidant being dependent on the substrate. The reaction proceeds through an external nucleophilic attack (Br -) on a (π-allene)palladium complex to produce a (π-allyl)palladium intermediate. Subsequent intramolecular attack by the second internal nucleophile gives the product. The intermediate (π-allyl)palladium complexes were isolated and characterized. The scope and limitation of the reaction were studied together with its mechanism and selectivity, under different reaction conditions.

Redox-Induced Aromatic C–H Bond Functionalization in Metal Complex Catalysis from the Electrochemical Point of View

“…Reoxidants such as Cu(OAc) 2 , AgOAc, Ag 2 CO 3 , and 1,4-benzoquinone typically mediate the Pd(0)/Pd(II) catalysis of a dehydrogenative Heck reaction [80]. For example, intramolecular Pd(II) catalyzed 1,2-addition to allenes (Scheme 8).…”

“…A subsequent intramolecular attack by the second internal nucleophile gives the product. The intermediate (π-allyl)palladium complexes were isolated and characterized [80]. Two different reoxidants for this Pd(0)/Pd(II) system (1,4-benzoquinone or Cu(OAc) 2 ) were used.…”

Palladium(II)‐Catalyzed Oxidative Carbocyclization of Aza‐Enallenes

“…[11] We have previously reported various palladium-catalyzed transformations of allenes. [12][13][14] These studies have focused on a variety of C-allenyl compounds that contain olefinic side chains. Such substrates are well-suited for palladium(II)-catalyzed carbon À carbon bond-forming oxidative cyclization reactions, [13] as well as palladium(0)-catalyzed cyclization reactions.…”

Metal‐Catalyzed Cycloetherification Reactions of β,γ‐ and γ,δ‐Allendiols: Chemo‐, Regio‐, and Stereocontrol in the Synthesis of Oxacycles

“…[15] The treatment of b,g-allenic diols 3 a and 3 c (bearing a methyl group on the allene group) with lithium bromide by using a Pd-Cu bimetallic catalytic system selectively led to bromoetherification products 20 in reasonable yields of the isolated products that ensued from 6-endo-trig cyclization. We also tested the reactivity of b,g-allendiols 3 b and 3 d bearing a phenyl rather than a methyl allene substituent.…”