Tunable Synthesis of 2-Ene-1,4-diones, 4-Hydroxycyclopent-2-en-1-ones, and 2-(Furan-3-yl)acetamides via Palladium-Catalyzed Cascade Reactions of Allenols

Abstract

An efficient and regioselective synthesis of 2ene-1,4-diones, 4-hydroxycyclopent-2-en-1-ones, or 2-(furan-3yl)acetamides is successfully realized through palladiumcatalyzed one-pot multicomponent reactions of allenols with aryl iodides and carbon monoxide in the presence of tertiary amines. Interestingly, the selectivity depends on the substitution patterns of the allenol substrates. To be specific, from the reaction of allenols with no substituent attached on the internal position of the allenic moiety, 2-ene-1,4-diones or 4hydroxycyclopent-2-en-1-ones were formed selectively through carbonylation of aryl iodide followed by acylation of allenol with the in situ formed acyl palladium species, β-hydride elimination of the in situ formed allyl palladium complex, and further tautomerization or intramolecular aldol reaction. From the reaction of allenols bearing a substituent at the internal position of the allenic unit, on the other hand, diversely substituted 2-(furan-3-yl)acetamides were formed through a cascade process combining carbonylation of aryl iodide, acylation, and carbonylation of allenol followed by intramolecular condensation and amination by tertiary amine featuring an oxidant-free C−N bond cleavage.

Deciphering the Chameleonic Chemistry of Allenols: Breaking the Taboo of a Onetime Esoteric Functionality

“…Taking advantage of the low redox potential of palladium, many reports have appeared describing cascade processes of allenols promoted by palladium salts. − Thus, a multicomponent reaction of α-allenols 414 with aryl iodides 415 , aliphatic alcohols 416 and carbon monoxide led to tetrasubstituted furans 417 through an oxidative addition/carbonylation reaction sequence (Scheme , reaction a) . In a similar approach, the presence of tertiary amines 418 instead alcohols 416 in the reaction media provided the corresponding methylene acetamide-decorated furans 419 (Scheme , reaction b) . Gong and collaborators have reported a related methodology using allenol 414a , aryl iodides 415 and imines 420 as reaction partners also under palladium catalysis to provide an extense family of oxazolidine derivatives 421 .…”

“… 289 In a similar approach, the presence of tertiary amines 418 instead alcohols 416 in the reaction media provided the corresponding methylene acetamide-decorated furans 419 ( Scheme 71 , reaction b). 290 Gong and collaborators have reported a related methodology using allenol 414a , aryl iodides 415 and imines 420 as reaction partners also under palladium catalysis to provide an extense family of oxazolidine derivatives 421 . In this case, the proposed reaction mechanism includes carbopalladation onto the central carbon atom of the allene moiety, nucleophilic attack of the oxygen onto the C–C double bond of the imine, and latter ring closing step through nucleophilic addition of the nitrogen onto the inner π-allylic carbon atom ( Scheme 71 , reaction c).…”

π-Allylpalladium Complexes in Synthesis: An Update

“…They were selectively obtained, depending on the allenol structure, in a palladium-catalyzed one-pot multicomponent reaction between the allenol, aryl iodides, and CO in the presence of a tertiary amine. 69 In particular, when 1,2dienols not substituted at the internal position (R 3 = H) were used, the reaction afforded 2-ene-1,4-diones 172 (Scheme 50, path a) or 4-hydroxycyclopent-2-enones 173 (Scheme 50, path b) in a selective manner. In this case, the aryl iodide carbonylation produces an acylpalladium species that reacts with the allenol.…”

Electrochemical stereoselective synthesis of polysubstituted 1,4-dicarbonyl Z-alkenes via three-component coupling of sulfoxonium ylides and alkynes with water

“…3 Moreover, the synthetic methodologies of 1,4-dicarbonyl alkenes have attracted considerable attention, and remarkable progress has been made over the past few decades. 4 Conventionally, 1,4-dicarbonyl Z -alkenes were synthesized by oxidative ring opening of furan and thiophene derivatives, breakdown of α-diazo carbonyl compounds, and the Wittig reaction. 5,6 Recently, the Maulide group developed Ru-catalyzed cross olefination of diazo compounds with sulfoxonium ylides to give disubstituted 1,4-dicarbonyl Z -alkenes.…”