Preparation of 2-Amino-5-homoallylfurans via Palladium-Catalyzed Tandem Cycloisomerization/Heck-Type Coupling of Homoallenyl Amides with Allyltrialkylsilanes

Abstract

The direct access to 2-amino-5-homoallylfurans has been realized by a palladium-catalyzed tandem cycloisomerization/Heck-type coupling between homoallenyl amides and allyltrialkylsilanes, using a novel DDQ/MnO combination as the efficient oxidant. The reaction exclusively affords γ-allylation products in good to excellent yields with broad substrate scope under exceptionally mild reaction conditions. It represents one of the rare examples of the Pd-catalyzed intermolecular Heck-type coupling of allytrialkylsilanes terminated by β-silyl elimination, thus complementing traditional allylation methods because of the excellent γ-selectivity.

Recent Development in Palladium-Catalyzed Domino Reactions: Access to Materials and Biologically Important Carbo- and Heterocycles

“…Furan is an important five-membered heterocycle, commonly found in chemical, material, and biological areas. Particularly, 2-aminofurans have attracted numerous attention because they have been used as antibacterial agents, inhibitors for activated cdc42-associated tyrosine kinase1 (ACK1), etc . Zhu and col. described a new domino cycloisomerization/​allylation of homoallenyl amides with allyltrialkylsilanes catalyzed by palladium to synthesize 2-amino-5-homoallylfurans.…”

“…This process provided exclusively γ-allylation products in good to excellent yields, allowing a broad substrate scope under mild reaction conditions (Scheme ). The terminating step consisted in a β-silyl elimination, affording the precatalytic Pd 0 species …”

“…The terminating step consisted in a β-silyl elimination affording the precatalytic Pd 0 species. 162 In the same context, this group developed a synthesis of 2-amino-5-(sulfonylmethyl)furans through cyclizative sulfonylation of homoallenyl amides with sodium sulfinates catalyzed by palladium acetate (10 mol%) with PhI(O2CCF3)2 (1.2 equiv) as oxidant at room temperature. 163 Scheme 107.…”

Allenamides Playing Domino: A Redox‐Neutral Photocatalytic Synthesis of Functionalized 2‐Aminofurans

“…Besides traditional protocols often employing stoichiometric or more than stoichiometric mediators, [3] more sustainable catalytic processes have been recently developed [4] . Among them, the most noteworthy processes employ α,β‐unsaturated nitriles, [4a–b,s–t] ynamides, [4d,k,m] α‐diazo carbonyl compounds, [4j–k] the tricomponent mixture aldehyde/isocyanide/electron‐poor alkyne, [4n–p] furans, [4r] α‐haloketones with tertiary amines or enamines, [4q] allenylamides [4l] or homoallenyl amides [4e–i] (Scheme 1). All the reported protocols generally require properly functionalized and not commonly available substrates, noble metal catalysts in high loadings, excess reagents, high temperatures or environmentally unfriendly solvents, resulting in cost and toxicity concerns, poor functional group compatibility and narrow applicability.…”

“…The novelty of the designed synthetic approach also lies in the use of N ‐substituted allenamides 2 as substrates, which have never been used in the construction of 2‐aminofurans. Conversely, the already reported procedures invariably exploit C ‐substituted allenes as starting materials [3e,4e–i,l] . Heteroatom‐substituted allenes, [9] in particular nitrogen‐substituted [10] ones, are characterized by a peculiar reactivity.…”