Phosphine-catalyzed tandem reaction of allenoates with nitroalkenes

A P(p-FC(6)H(4))(3)-catalyzed tandem reaction between ethyl 2,3-butadienoate and nitroalkenes has been developed, which involves a [3 + 2] cycloaddition and a subsequent umpolung addition. The asymmetric version of this tandem reaction has also been investigated by using chiral phosphanes.     

Phosphine-catalyzed nitroaldol reactions

Trialkyl phosphines and electron-rich triaryl phosphines are excellent catalysts for the nitroaldol (Henry) reaction. Aryl and alkyl aldehydes participate well in the reaction with nitromethane providing good yields of product. Care should be exercised in the use of phosphine-metal complexes as catalysts for the nitroaldol reaction, as the phosphine can alone function as the catalyst.     

Phosphine-catalyzed domino reaction: an efficient method for the synthesis of highly functionalized spirooxazolines

A novel phosphine-catalyzed intermolecular [3 + 2] cycloaddition of ynones and N-substituted isatins was developed. In this reaction, substituted ynones, serving as a C(3) synthon, were successfully applied in intermolecular annulation reactions. A number of functionalized spirooxazolines were obtained in high yields and stereoselectivity.     

Phosphine-catalyzed construction of sulfur heterocycles

A simple and efficient method for constructing sulfur heterocycles was developed using a phosphine-catalyzed tandem umpolung addition and intramolecular cyclization of bifunctional sulfur pronucleophiles on arylpropiolates. The reaction offers a promising route to synthetically useful as well as biologically active heterocycles under neutral conditions.     

Phosphine-catalyzed bishydrophosphorylation of electron-deficient alkynes

Tertiary phosphines (n-Bu₃P, Ph₃P) efficiently catalyze the vicinal bis-addition of dialkyl phosphites and diaryl phosphine oxides to alkynoates though the tandem α-umpolung/β-Michael addition. This reaction offers a simple metal-free method for gram-scale preparation of practically useful bisphosphonates and bisphosphine oxides under mild conditions with high atom economy and selectivity.     

Phosphine-catalyzed synthesis of highly functionalized coumarins

2-Styrenyl allenoates are converted into cyclopentene-fused dihydrocoumarins through phosphine-catalyzed regio- and diastereoselective [3 + 2] cycloadditions. Remarkably, changing the solvent from THF to benzene promotes the conversion of the 2-(2-nitrostyrenyl) allenoate into a tricyclic nitronate through a previously undocumented mode of phosphine catalysis. This nitronate was subjected to efficient face-, regio-, and exo-selective 1,3-dipolar cycloadditions to provide tetracyclic coumarin derivatives.     

Phosphine-catalyzed synthesis of 1,3-dioxan-4-ylidenes

[reaction: see text] A phosphine-catalyzed reaction of an allenoate with aldehydes furnished (2,6-diaryl-[1,3]dioxan-4-ylidene)-acetates 4 in excellent to moderate yields with complete diastereoselectivity and high E/Z-selectivities. Upon removal of the acetal functionality in this domino reaction product 4, delta-hydroxy-beta-ketoester 11 was obtained. The reported vinylphosphonium-based approach provides a new way to achieve a synthesis of delta-hydroxy-beta-ketoesters that differs from the classical dianion-based approach.     

Phosphine-catalyzed [3+3] annulation reaction of modified tert-butyl allylic carbonates and substituted alkylidenemalononitriles

A phosphine-catalyzed [3+3] annulation reaction of modified tert-butyl allylic carbonates with various alkylidenemalononitriles to form cyclohexenes was developed. The use of protic solvent is crucial in this reaction. When non-polar solvent, toluene or xylene, was used, only non-cyclized product was obtained.     

Phosphine-catalyzed acyl-transfer of heteroaryl ketones for the construction of N-fused heterocycles

An inexpensive phosphine catalyst was used effectively for a transition-metal-free acyl-transfer of N-containing heteroaryl ketones for the rapid synthesis of N-fused heterocycles. The key pre-aromatic spirocyclic intermediate initialized by the single electron transfer(SET) process of Togni’s reagent Ⅱ promoted by the tertiary phosphine resulted in an intriguing and alternative tactic for the cleavage of C–C bonds. By using inexpensive tertiary phosphine as the catalyst, this skeleton-reorganiz...     

Phosphine-catalyzed enantioselective [3+2] annulations of 2,3-butadienoates with imines

The first systematic screening of chiral phosphines in the cycloaddition reaction between 2,3-butadienoates and arylimines has led to the identification of fairly efficient catalysts. 2-Aryl-3-pyrrolines have been obtained with enantiomeric excesses up to 64%. In one instance, the enantiomeric excess could be increased to 91% ee by combining the enantioselective cyclization reaction with a crystallization step.     

Phosphine-catalyzed cycloadditions of allenic ketones: new substrates for nucleophilic catalysis

A range of phosphine-catalyzed cycloaddition reactions of allenic ketones have been studied, extending the scope of these processes from the more widely used 2,3-butadienoates to allow access to a number of synthetically useful products. Reaction of allenyl methyl ketone 4 with exo-enones afforded spirocyclic compounds in good regioselectivity and promising enantioselectivity via a [2 + 3] cycloaddtion. Aromatic allenyl ketones undergo a phosphine-promoted dimerization to afford functionalized pyrans, leading to a formal [2 + 4] Diels-Alder product, but did not react in the [2 + 3] cycloaddition. The results from other reactions that had found utility with 2,3-butadienoates are also reported.     

Phosphine-catalyzed regiospecific allylic amination and dynamic kinetic resolution of Morita-Baylis-Hillman acetates

Exposure of Morita-Baylis-Hillman (MBH) acetates to tertiary phosphine catalysts in the presence of 4,5-dichlorophthalimide enables regiospecific allylic substitution through a tandem S(N)2'-S(N)2' mechanism. Through the use of the chiral phosphine catalyst (R)-Cl-MeO-BIPHEP, chiral racemic MBH acetate 4 is converted to the corresponding allylic amination product in 80% yield and 56% enantiomeric excess, thus establishing the feasibility of dynamic kinetic resolution. [reaction: see text]     

Phosphine-catalyzed regioselective heteroaromatization between activated alkynes and isocyanides leading to pyrroles

The organophosphine catalyzed reaction of activated alkynes with isocyanides produces the corresponding heteroaromatization products, pyrroles, regioselectively in good yields. The reaction proceeds most probably through the 1,4-addition of the nucleophilic phosphine catalyst to the alkynes, followed by a [3+2] cycloaddition between the resulting alkenyl phosphine intermediates and a carbanion derived from the isocyanides.     

Phosphine-catalyzed alpha-P-addition on activated alkynes: A new route to P-C-P backbones

n-Tributylphosphine was found to efficiently catalyze the alpha-P addition of H-phosphonates, H-phosphinates, and H-phosphine oxide pronucleophiles on alkynes bearing phosphane oxide activating moieties. The reaction leads to 2-aryl-1-vinyl-1,1-diphosphane dioxide derivatives in good yields affording a new route to P-C-P backbones. The products of this reaction are easily converted to biologically important 1,1-bis-phosphonates analogues.     

Phosphine-catalyzed allylic substitution of Morita-Baylis-Hillman acetates: synthesis of N-protected beta-aminophosphonic acid esters

A series of N-protected beta-amino phosphonic acid esters have been prepared by phosphine-catalyzed allylic substitution of 2-(diethylphosphonyl)-substituted allylic acetates employing 4,5-dichlorophthalimide as nucleophilic partner. These organocatalytic allylic substitutions exhibit exceptionally high levels of regiospecificity by virtue of a tandem S(N)2'-S(N)2' mechanism.     

Phosphine-catalyzed one-pot synthesis of cyclopentenes from electron-deficient allene,malononitrile and aromatic aldehydes

A three component reaction of aryl aldehydes and malononitrile with ethyl 2,3-butadienoate catalyzed by triphenylphosphine has been developed. The reaction furnishes highly functionalized cyclopentenes in moderate to good yields in a one-pot process.     

Phosphine-catalyzed dearomative [3+2] annulation of 3-nitroindoles and allenoates

The efficient phosphine-catalyzed dearomative [3+2] annulation of 3-nitroindoles with allenoates has been successfully developed, providing a facile access to cyclopenta[b]indolines with good to excellent yields and high diastereoselectivities. This strategy features mild reaction conditions, high functional group tolerance, and scalability. Additionally, the 2-nitrobenzofuran and 2-nitrobenzothiophene were good dearomative [3+2] annulation partners.     

Phosphine-catalyzed annulation of thioamides and 2-alkynoates: a new synthesis of thiazolines

The annulation of thioamides with 2-alkynoates and 2,3-dienoates under the catalysis of tri-n-butylphosphine was described. The annulation reaction provided a new entry to thiazolines, particularly those with 2-aryl substituents.