Phosphane-Catalyzed Umpolung Addition Reaction of Nucleophiles to Ethyl 2-Methyl-2,3-butadienoate

Phosphine-Catalyzed Ring-Opening Regioselective Addition of Cyclopropenones with Amides

A series of amides, including α-bromo hydroxamates, N-alkoxyamides, and N-aryloxyamides, were subjected to phosphine-catalyzed ring-opening O-selective addition with cyclopropenones, producing various special α,β-unsaturated esters containing oxime ether motif, in moderate to excellent yields, with high regioselectivity, and exclusive O-selectivity. The methodology is highly atom-economical, with simple operation procedures, and compatible with a wide substrate scope (more than 44 examples).

Synthesis of 3,4-Disubstituted Maleimide Derivatives via Phosphine-Catalyzed Isomerization of α-Succinimide-Substituted Allenoates Cascade γ'-Addition with Aryl Imines

3,4-disubstituted maleimides find wide applications in various pharmacologically active compounds. This study presents a highly effective approach for synthesizing derivatives of 3,4-disubstituted maleimides through the direct isomerization of α-succinimide-substituted allenoates, followed by a cascade γ'-addition and aryl imines using PR3 as a catalyst. The resulting series of 3,4-disubstituted maleimides exhibited excellent stereoselectivities, achieving yields of up to 86%. To our knowledge, the phosphine-mediated γ'-addition reaction of allenoates is seldom reported.

Vinylogous Elimination/C-H Functionalization/Allylation Cascade Reaction of Allenoate Adducts: Synthesis of Ring-Fused Dihydropyridinones

A palladium-catalyzed cascade reaction of β'-allenoate adducts with aryl/heteroaryl carboxamides through a vinylogous elimination/C-H functionalization/intramolecular allylation reaction sequence has been developed with high Z stereoselectivity. Various ring-fused dihydropyridinones bearing an α,β-unsaturated ester substituent are obtained. It is the first example of application of the allenoate adducts to C-H functionalization annulations as practical precursors of hard-to-get functionalized electron-deficient 1,3-butadienes. Using air as the terminal oxidant also shows a great advantage in environmental friendliness.

Phosphine-Catalyzed (4+1) Annulation: Rearrangement of Allenylic Carbamates to 3-Pyrrolines through Phosphonium Diene Intermediates

We have developed a phosphine-catalyzed (4+1) annulative rearrangement for the preparation of 3-pyrrolines from allenylic carbamates via phosphonium diene intermediates. We employed this methodology to synthesize an array of 1,3-disubstituted- and 1,2,3-trisubstituted-3-pyrrolines, including the often difficult to prepare 2-alkyl variants. A mechanistic investigation employing allenylic acetates and mononucleophiles unexpectedly unveiled that a phosphine-catalyzed (4+1) reaction for the construction of cyclopentene products, previously reported by Tong, might not occur through a phosphonium diene, as had been proposed, but rather through multiple mechanisms working in concert. Consequently, our phosphine-catalyzed rearrangement is most likely the first transformation to involve the unequivocal formation of a phosphonium diene intermediate along the reaction pathway. To demonstrate the synthetic utility of this newly developed reaction, we have completed concise formal syntheses of the pyrrolizidine alkaloids (±)-trachelanthamidine and (±)-supinidine.

Phosphine-catalyzed (3+2)/(2+3) sequential annulation involving a triple nucleophilic addition reaction of γ-vinyl allenoates

A phosphine-catalyzed (3+2)/(2+3) sequential annulation involving a triple nucleophilic addition reaction of γ-vinyl allenoates was successfully developed. The reaction provided efficient and more practical access to functionalized hydropyrroloimidazolones with good to excellent yields under mild reaction conditions. Notably, γ-vinyl allenoate served as a triple-electrophilic intermediate in this protocol.

Phosphine Organocatalysis

The hallmark of nucleophilic phosphine catalysis is the initial nucleophilic addition of a phosphine to an electrophilic starting material, producing a reactive zwitterionic intermediate, generally under mild conditions. In this Review, we classify nucleophilic phosphine catalysis reactions in terms of their electrophilic components. In the majority of cases, these electrophiles possess carbon-carbon multiple bonds: alkenes (section 2), allenes (section 3), alkynes (section 4), and Morita-Baylis-Hillman (MBH) alcohol derivatives (MBHADs; section 5). Within each of these sections, the reactions are compiled based on the nature of the second starting material-nucleophiles, dinucleophiles, electrophiles, and electrophile-nucleophiles. Nucleophilic phosphine catalysis reactions that occur via the initial addition to starting materials that do not possess carbon-carbon multiple bonds are collated in section 6. Although not catalytic in the phosphine, the formation of ylides through the nucleophilic addition of phosphines to carbon-carbon multiple bond-containing compounds is intimately related to the catalysis and is discussed in section 7. Finally, section 8 compiles miscellaneous topics, including annulations of the Hüisgen zwitterion, phosphine-mediated reductions, iminophosphorane organocatalysis, and catalytic variants of classical phosphine oxide-generating reactions.

An elimination/Heck coupling/allylation cascade reaction: synthesis of 2,3-dihydrobenzofurans from allenoate adducts

A highly regio- and stereoselective Pd-catalyzed cascade reaction of allenoate adducts has been developed. Various allenoate adducts of phosphine-catalyzed addition of allenoates are found to be efficient substrates for the preparation of 2,3-dihydrobenzofuran. It is the first example of allenoate adducts used as ideal and practical precursors of hard-to-get functionalized 1,3-butadienes for heterocycle synthesis.

Hydroxy-assisted regio- and stereoselective synthesis of functionalized alkenes via phosphine-catalyzed β′-umpolung addition of o-hydroxy aromatic aldimines to allenoates

An unprecedented β′-umpolung addition of o-hydroxy aromatic aldimines with allenoates has been developed under the catalysis of phosphine.

Phosphine-catalysed α-umpolung addition of nucleophiles to δ-acetoxy allenoates: stereoselective synthesis of 2,4-dienoates

The first example of phosphine-catalyzed α-umpolung addition of nucleophiles to allenoates is described, which features the use of δ-acetoxy allenoate to generate a 3-phosphonium-2,4-dienoate intermediate, thus facilitating the α-umpolung addition of nucleophiles.

Phosphine catalysed (5 + 1) annulation of ynone/cinnamates with primary amines

The (5 + 1) annulation of ynone/cinnamates with protected primary amines gives rise to various heterocycles in good to excellent yields under phosphine catalysis.

Reaction of allene esters with Selectfluor/TMSX (X = I, Br, Cl) and Selectfluor/NH4SCN: Competing oxidative/electrophilic dihalogenation and nucleophilic/conjugate addition

Reaction of benzyl and ethyl allenoates with TMSX (X = I, Br, Cl) and with NH₄SCN were investigated in MeCN, DMF, and in imidazolium ionic liquids [BMIM][NTf₂] and [BMIM][PF₆] as solvent, in the presence and absence of Selectfluor. Comparative product analysis studies demonstrate that the ability of Selectflour to promote oxidative/electrophilic dihalogenation/dithiocyanation with TMSX/NH₄SCN (as observed previously for 1-arylallenes) is diminished in allenoates, most significantly in reactions with TMSCl, and essentially disappearing in reactions with NH₄SCN, in favor of nucleophilic/conjugate addition. The study underscores the contrasting reactivity patterns in 1-arylallenes and allenoates toward electrophilic and nucleophilic additions in halofunctionalization with TMSX/Selectfluor and thiocyanation reactions with NH₄SCN/Selectfluor. These competing pathways are influenced by the nature of the anion, allene structure, and the choice of solvent.

Phosphine-catalyzed regioselective Michael addition to allenoates

The first phosphine catalysed Michael addition of arylcyanoacetates to allenoates has been developed, and the β-selective products with a quaternary center were obtained in excellent yields.

Convenient synthesis of substituted tetrahydrofuran via Lewis base catalyzed [3 + 2] domino reactions

A DABCO catalyzed domino reaction between 3-oxo-4-(2-oxoindolin-3-ylidene) butanoates and allenoates furnished 2,3,5-substituted tetrahydrofuran furan derivatives bearing oxindole moiety and two exocyclic double bonds in high yield.

Advances in nucleophilic phosphine catalysis of alkenes, allenes, alkynes, and MBHADs

In nucleophilic phosphine catalysis, tertiary phosphines undergo conjugate additions to activated carbon-carbon multiple bonds to form β-phosphonium enolates, β-phosphonium dienolates, β-phosphonium enoates, and vinyl phosphonium ylides as intermediates. When these reactive zwitterionic species react with nucleophiles and electrophiles, they may generate carbo- and heterocycles with multifarious molecular architectures. This article describes the reactivities of these phosphonium zwitterions, the applications of phosphine catalysis in the syntheses of biologically active compounds and natural products, and recent developments in the enantioselective phosphine catalysis.

Phosphine-initiated general base catalysis: facile access to benzannulated 1,3-diheteroatom five-membered rings via double-Michael reactions of allenes

General base-catalyzed double-Michael reactions of allenes with various dinucleophiles are described. The reactions are facilitated most efficiently by a catalytic amount of trimethylphosphine, affording six types of C2-functionalized benzannulated five-membered heterocycles: benzimidazolines, benzoxazolines, benzothiazolines, 1,3-benzodioxoles, 1,3-benzoxathioles, and 1,3-benzodithioles. This atom-economical reaction is operationally simple and provides the product heterocycles in good to excellent yields. Careful mechanistic studies unveiled the phosphine-triggered general base catalysis pathway. Furthermore, the double-Michael reaction can serve as an alternative method for the selective monoketalization of β-diketones.