1,3,5-Triaza-7-phosphaadamantane (PTA): A Practical and Versatile Nucleophilic Phosphine Organocatalyst

Novel three-dimensional coordination polymer of 2-(1,3,5-triaza-7-phosphoniatricyclo[3.3.1.13,7]decan-7-yl)ethanoic acid with silver(I) tetrafluoroborate

An AgI-based coordination polymer (CP), namely, poly[[[μ3-2-(1,3,5-triaza-7-phosphoniatricyclo[3.3.1.13,7]decan-7-yl)ethanoate-κ4 N:N′:O,O′]silver(I)] tetrafluoroborate], {[Ag(C9H16N3O2P)]BF4} n , was synthesized in an aqueous solution of zwitterionic 2-(1,3,5-triaza-7-phosphoniatricyclo[3.3.1.13,7]decan-7-yl)ethanoate (L) and AgBF4 with exclusion of light at room temperature. The colourless and light-insensitive CP crystallized in the monoclinic space group Cc. The asymmetric unit consists of an AgI cation, the zwitterionic L ligand and a BF4 − counter-ion. Each AgI ion is coordinated by two carboxylate oxygen atoms in a chelating coordination mode, as well as one of the nitrogen atoms of two neighbouring L ligands. The crystal structure of the CP was classified as a unique three-dimensional arrangement. The CP was also characterized in aqueous solutions by multinuclear NMR and HRMS spectroscopies and elemental analysis.

Phosphine-Catalyzed Asymmetric Tandem Isomerization/Annulation of Allyl Amines with Allenoates: Enantioselective Annulation of a Saturated C-N Bond

Under catalysis by chiral phosphine, an asymmetric isomerization/annulation cascade reaction of allylamines with allenoates was realized. A wide range of γ-substituted allenoates were tolerated to afford chiral pyrroline derivatives in high yields with excellent enantioselectivities. In the reaction, isomerization of readily available N-allylamines to reactive aliphatic imines through a 1,4-proton shift is a key step, which circumvents the isolation of highly unstable alkyl N-sulfonylimines.

Phosphine-catalyzed [3 + 2] annulation of β-sulfonamido-substituted enones with trans-α-cyano-α,β-unsaturated ketones for the synthesis of highly substituted pyrrolidines

To synthesize highly substituted pyrrolidines, we developed a phosphine-catalyzed [3 + 2] annulation of β-sulfonamido-substituted enones with trans-α-cyano-α,β-unsaturated ketones. We prepared a series of pyrrolidines under mild conditions with high yields and moderate-to-good diastereoselectivities. A catalytic mechanism for this reaction is suggested.

To synthesize highly substituted pyrrolidines, we developed a phosphine-catalyzed [3 + 2] annulation of β-sulfonamido-substituted enones with trans-α-cyano-α,β-unsaturated ketones.

Synthesis of heterocyclic compounds through nucleophilic phosphine catalysis

Nucleophilic phosphine catalysis is a practical and powerful tool for the synthesis of various heterocyclic compounds with the advantages of environmentally friendly, metal-free, and mild reaction conditions. The present report summarizes the construction of four to eight-membered heterocyclic compounds containing nitrogen, oxygen and sulphur atoms through phosphine-catalyzed intramolecular annulations and intermolecular [2+2], [3+2], [4+1], [3+1+1], [5+1], [4+2], [2+2+2], [3+3], [4+3] and [3+2+3] annulations of electron-deficient alkenes, allenes, alkynes and Morita-Baylis-Hillman carbonates.

Mechanochemical P-derivatization of 1,3,5-Triaza-7-Phosphaadamantane (PTA) and Silver-Based Coordination Polymers Obtained from the Resulting Phosphabetaines

We have described earlier that in aqueous solutions, the reaction of 1,3,5-triaza-7-phosphaadamantane (PTA) with maleic acid yielded a phosphonium-alkanoate zwitterion. The same reaction with 2-methylmaleic acid (citraconic acid) proceeded much slower. It is reported here, that in the case of glutaconic and itaconic acids (constitutional isomers of citraconic acid), formation of the corresponding phosphabetaines requires significantly shorter reaction times. The new phosphabetaines were isolated and characterized by elemental analysis, multinuclear NMR spectroscopy and ESI-MS spectrometry. Furthermore, their molecular structures in the solid state were determined by single crystal X-ray diffraction (SC-XRD). Synthesis of the phosphabetaines from PTA and unsaturated dicarboxylic acids was also carried out mechanochemically with the use of a planetary ball mill, and the characteristics of the syntheses in solvent and under solvent-free conditions were compared. In aqueous solutions, the reaction of the new phosphabetaines with Ag(CF3SO3) yielded Ag(I)-based coordination polymers. According to the SC-XRD results, in these polymers the Ag(I)-ion coordinates to the N and O donor atoms of the ligands; however, Ag(I)-Ag(I) interactions were also identified. The Ag(I)-based coordination polymer (CP1.2) formed with the glutaconyl derivative of PTA (1) showed considerable antimicrobial activity against both Gram-negative and Gram-positive bacteria and yeast strains.

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 [4+1] Cycloadditions of Allenes with Methyl Ketimines, Enamines, and a Primary Amine

Unprecedented phosphine-catalyzed [4+1] cycloadditions of allenyl imides have been discovered using various N-based substrates including methyl ketimines, enamines, and a primary amine. These transformations provide a one-pot access to cyclopentenoyl enamines and imines, or (chiral) γ-lactams through two geminal C-C bond or two C-N bond formations, respectively. Several P-based key intermediates including a 1,4-(bis)electrophilic α,β-unsaturated ketenyl phosphonium species have been detected by ³¹ P NMR and HRMS analyses, which shed light on the postulated catalytic cycle. The synthetic utility of this new chemistry has been demonstrated through a gram-scaling up of the catalytic reaction as well as regioselective hydrogenation and double condensation to form cyclopentanoyl enamines and fused pyrazole building blocks, respectively.

One-Pot Synthesis of Aza-Morita-Baylis-Hillman Adducts via Zinc-Mediated Allylation of 4-Bromocrotonates and Imines

An approach to the synthetically valuable β-substituted aza-Morita-Baylis-Hillman (MBH) type products, through zinc-mediated allylation of imines with 4-bromocrotonates followed by subsequent isomerization of the double bond, was developed. Complementary to classical MBH reaction, this reaction utilizes easily available 4-bromocrotonates as the reaction partners, providing a rapid alternative to the traditional use of α,β-unsaturated carbonyl compounds. The short reaction time, one-pot operation, broad substrate scopes, gram-scale synthesis, and synthetic application exemplified the utility and practicability of this method.

Chemoselective and Highly Rate Accelerated Intramolecular Aza-Morita-Baylis-Hillman Reaction

Despite being a very useful C-C bond forming and highly applicative reaction, Morita-Baylis-Hillman (MBH) reaction has been limited by its excessive slow reaction rate, including its intramolecular version. In certain cases, reaction time may even go to weeks and months. A highly chemoselective and rate accelerated intramolecular MBH reaction of just 15 min has been developed. The product dihydroquinoline, being unstable, was converted to an important quinoline framework. In some cases IMBH adducts were isolable, thus confirming the reaction path. Control experiments toward mechanism investigation have been carried out. Use of sodium sulfide has emerged as a rate accelerating catalyst in DMF-EtOH solvent system. Reaction intermediate for IMBH pathway was isolated and characterized. Other aspects such as the application of IMBH adduct for Michael addition and amidation have also been carried out.

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.

Nafion®-Containing Solid Lipid Nanoparticles as a Tool for Anticancer Pt Delivery: Preliminary Studies

Preliminary studies of nanoparticles based on the perfluorosulfonic acid resin Nafion have been carried out with the aim of establishing an ionic connection with the protonable phosphine 1,3,5-triaza-7-phosphaadamantane (PTA), suitable for the coordination of platinum. Nafion-containing nanoparticles (NAF) were produced by homogenization followed by ultrasonication method. After production, NAF were characterized in terms of size, morphology, andin vitrocytotoxicity. The PCS studies showed that theZ-average mean diameter was around 250 nm. Moreover, the polydispersity index showed a monodimensional distribution of nanoparticles. Cryo-TEM analysis showed a uniform and homogenous population of particles, characterized by the presence of both ovoidal and needle-like structures. To evaluate thein vitrocytotoxicity, NAF were tested on human cancer cell lines K562 and A2780. No cytotoxic effect was found on both cell lines. By13P-NMR measures, it is here proved that the strongly acidic sulfonic groups of Nafion-containing nanoparticles (NAF) can act as protonating agents for PTA. The protonation occurs selectively at nitrogen; hence protonated PTA maintains its ability to coordinate platinum via its phosphorus atom.

Morita-Baylis-Hillman reaction of acrylamide with isatin derivatives

The Morita–Baylis–Hillman reaction of acrylamide, as an activated alkene, has seen little development due to its low reactivity. We have developed the reaction using isatin derivatives with acrylamide, DABCO as a promoter and phenol as an additive in acetonitrile. The corresponding aza version with acrylate and acrylonitrile has also been developed resulting in high product yields.

Anti-cancer palladium complexes: a focus on PdX2L2, palladacycles and related complexes

Much success has been achieved with platinum-based chemotherapeutic agents, i.e. through interactions with DNA. The long-term application of Pt complexes is thwarted by issues, leading scientists to examine other metals such as palladium which could exhibit complementary modes of action (given emphasis wherever known). Over the last 10 years several research groups have focused on the application of an eclectic array of palladium complexes (of the type PdX2L2, palladacycles and related structures) as potential anti-cancer agents. This review therefore provides readers with an up to date account of the advances that have taken place over the past several decades.

The aza-Morita-Baylis-Hillman reaction: a mechanistic and kinetic study

The aza-Morita-Baylis-Hillman (aza-MBH) reaction has been studied in a variety of solvents, a selection of imine substrates and with various combinations of PPh3 and para-nitrophenol as the catalyst system. The measured kinetic data indicates that the effects of solvent and protic co-catalyst are strongly interdependent. These results are most easily reconciled with a mechanistic model involving the reversible protonation of zwitterionic intermediates in the catalytic cycle, which is also supported by (31)P NMR spectroscopy and quantum chemical studies.

Phosphine-Catalyzed [3+2] and [4+3]Annulation Reactions of C,N-Cyclic Azomethine Imines with Allenoates

Phosphine-catalyzed [3+2] and [4+3]annulation reactions of C,N-cyclic azomethine imines with allenoates have been developed to give a variety of pharmaceutically attractive tetrahydroisoquinoline derivatives in moderate to excellent yields. The two distinct reaction pathways, [3+2] and [4+3]cyclization, depend on the nature of the nucleophilic phosphine and the allenoate. Generally, for α-alkylallenoates, the reactions always proceed with [3 +2]cyclization as the major pathway no matter what phosphine was used; for α-ArCH₂-substituted allenoates, the reaction pathway was controlled by the phosphine catalyst used.

The aza-Morita-Baylis-Hillman reaction of electronically and sterically deactivated substrates

The aza-Morita-Baylis-Hillman (azaMBH) reaction has been studied for electronically and sterically deactivated Michael acceptors. It is found that electronically deactivated systems can be converted with electron-rich phosphanes and pyridines as catalysts equally well. For sterically deactivated systems clearly better catalytic turnover can be achieved with pyridine catalysts. This is in accordance with the calculated affinities of the catalysts towards different Michael-acceptors.