Versatile Synthesis of Phospholides from Open-Chain Precursors. Application to Annelated Pyrrole– and Silole–Phosphole Rings

Reactions of Benzyl Phosphine Oxide/Sulfide with (COCl)2: Synthesis of Novel Acyl Chloride-Substituted Chlorophosphonium Ylides

New reactions of benzyl phosphine oxide/sulfide with oxalyl chloride are presented. The resulting reactive intermediates, acyl chloride-substituted chlorophosphonium ylides, are capable of undergoing esterification and Friedel-Crafts acylation reactions, ultimately yielding either methyl 2-(2-bromophenyl)-2-(diphenylphosphoryl)acetate or β-carbonyl-diarylphosphine oxide derivatives. Additionally, when an alkynyl group is contained in the acyl chloride-substituted chlorophosphonium ylide, intramolecular cyclization occurs, leading to the formation of a pair of trans- and cis-dichlorophosphonyl benzofulvene isomers. The generation process of acyl chloride-substituted chlorophosphonium ylide was carefully monitored by using 31P{1H} NMR spectroscopy, and a plausible reaction mechanism was proposed.

Enantioselective Synthesis of P-Chirogenic 1,2,3-Triazolobenzophospholes

An enantioselective synthesis of a new class of benzophosphole-based heterocycles bearing a fused triazole ring with enantioselectivities of ≤99% is reported. The key steps of the synthesis are based on an innovative stereospecific phosphinyl N → O migration of aminophosphine-boranes into phosphinites, followed by an intramolecular cyclization. Five X-ray structures of P-chirogenic triazolobenzophospholes and a gold(I) complex were established, for assigning absolute configurations, the stereochemistry of the reactions, and the placement of the triazole substituent at the syn position of the P center.

The Synthesis and Properties of Ladder-Type π-Conjugated Compounds with Pyrrole and Phosphole Rings

The phosphole ring is known as a useful building block for constructing π-conjugated organic materials. Here, we report ladder-type benzophospholo[3,2-b]indole (BPI) derivatives where the phosphole and the pyrrole rings are directly fused. Compounds 8a-8d with different aryl groups on the phosphorous center were successfully synthesized, and the solid-state structure of 8a was confirmed using X-ray crystallographic analysis. The BPIs exhibit relatively high fluorescence quantum yield (Φ 0.50-0.72) and demonstrate a larger Stokes shift compared with a series of benzophospholo[3,2-b]benzoheteroles. The benzophospholo[3,2-b]carbazole derivative 9, which possesses a benzene ring between the phosphole and the pyrrole rings of the BPI, was also synthesized, and its solid-state structure was confirmed using X-ray crystallographic analysis. Compound 9 was found to show a smaller Stokes shift compared with the BPI.

Synthesis of Photochromic Phosphines by Pd-Catalyzed Annulation Reaction of Alkynes Bearing Phosphinyl Substituent with a Silacyclopropene

The synthesis of phosphines with light controlled basicity is presented in this study. A methodological approach for the preparation of these unconventional photochromic phosphines based on a dithienylethene organic moiety is reported. It relies on the palladium-catalyzed annulation of alkynyl phosphines in the presence of a 2,3-Dithienylsilacyclopropene. Accordingly, a diphenyphosphino moiety is connected to the organic photochrome thanks to different linkers. Their influence on the photochromism and on the phosphinyl group basicity is studied and evaluated based on experimental an NMR descriptor as well as DFT calculations.

One-Step Synthesis of Benzophosphole Derivatives from Arylalkynes by Phosphenium-Dication-Mediated Sequential C-P/C-C Bond Forming Reaction

A metal-free, phosphenium-dication-mediated sequential C-P and C-C bond forming reaction has been developed. This protocol can provide concise access to the (di)benzophosphole derivatives in one synthetic operation from the readily available and simple arylalkynes and phosphinic acids. Application to the multiple cyclization reaction and the fully intermolecular three-component-coupling-type reaction are also described.

Facile Synthesis of the Dicyanophosphide Anion via Electrochemical Activation of White Phosphorus: An Avenue to Organophosphorus Compounds

Organophosphorus compounds (OPCs) have gained tremendous interest in the past decades due to their wide applications ranging from synthetic chemistry to materials and biological sciences. We describe herein a practical and versatile approach for the transformation of white phosphorus (P₄) into useful OPCs with high P atom economy via a key bridging anion [P(CN)₂]^-. This anion can be prepared on a gram scale directly from P₄ through an electrochemical process. A variety of OPCs involving phosphinidenes, cyclophosphanes, and phospholides have been made readily accessible from P₄ in a two-step manner. Our approach has a significant impact on the future preparation of OPCs in laboratory and industrial settings.

Ring Opening of Triflates Derived from Benzophospholan-3-one Oxides by Aryl Grignard Reagents as a Route to 2-Ethynylphenyl(diaryl)phosphine Oxides

A new simple method for the synthesis of 2-ethynylphenyl(diaryl)phosphine oxides via ring opening of benzophosphol-3-yl triflates has been developed. This process occurs via nucleophilic attack of a Grignard reagent at the phosphorus center, which results in ring opening and cleavage of a leaving group. The reaction proceeds under mild conditions and, within 15-60 min, leads to a library of previously unavailable 2-ethynylphenylphosphine oxides in yields up to 98%.

Metal-Catalyzed Haloalkynylation Reactions

Metal catalysis has revolutionized synthetic chemistry, leading to entirely new, very efficient transformations, which enable access to complex functionalized molecules. One such new transformation method is the haloalkynylation reaction, in which both a halogen atom and an alkynyl unit are transferred to an unsaturated carbon‐carbon bond. This minireview summarizes the development of metal‐catalyzed haloalkynylation reactions since their beginning about a decade ago. So far, arynes, alkenes and alkynes have been used as unsaturated systems and the reactivities of these systems are summarized in individual chapters of the minireview. Especially, the last few years have witnessed a rapid development due to gold‐catalyzed reactions. Here, we discuss how the choice of the catalytic system influences the regio‐ and stereoselectivity of the addition.

Visible-Light-Induced Oxidative C-H Functionalization of Unreactive Cycloalkanes, Alcohols, and Ethers with Alkynylphosphine Oxides into Benzo[b]phosphole Oxides under Photocatalyst-, Metal-, and Base-Free Conditions

We developed the radical cyclization/addition of alkynylphosphine oxides with easily available cycloalkanes, alcohols, and ethers using a visible-light and environmentally friendly synthetic strategy in the absence of photocatalyst at room temperature. This mild and metal- and base-free reaction provided a structurally varied set of significant benzo[b]phosphole oxides through sequential C-H functionalization in an atom-economical manner.

Concise Synthesis of Phospholene and Its P-Stereogenic Derivatives

A simple method to build phospholene derivatives has been achieved in a one-pot reaction with readily available o-alkynylaryl bromides and alkylphosphine oxides. This method is also applicable to synthesize P-stereogenic phospholenes, and the resulting chiral phosphine was utilized as a ligand for coordination chemistry.

Access to Substituted Thiophenes through Xanthate-Mediated Vinyl C(sp2)-Br Bond Cleavage and Heterocyclization of Bromoenynes

An environmentally sustainable strategy for the chemoselective heterocyclization of bromoenynes through a transition-metal-free sulfuration/cyclization process is reported. Using inexpensive and safe EtOCS₂K as a thiol surrogate and tetrabutylphosphonium bromide and H₂O as a mixed solvent, the reaction provided a range of substituted thiophenes in moderate to good yields. In addition, 2,3,4,5-tetrasubstituted thiophenes were able to be prepared under mild reaction conditions by electrophilic heterocyclization with NH₄I and EtOCS₂K in good yields.

Azobisisobutyronitrile-Initiated Oxidative C-H Functionalization of Simple Alcohols with Diaryl(arylethynyl)phosphine Oxides: A Metal-Free Approach toward Hydroxymethyl Benzo[b]phosphole Oxides and 6H-Indeno[2,1-b]phosphindole 5-Oxide Derivatives

The first metal-free and facile radical addition/cyclization of simple alcohols with diaryl(arylethynyl)phosphine oxides has been described with azobisisobutyronitrile as a radical initiator, affording an efficient and one-pot procedure to access a new class of hydroxymethyl benzo[b]phosphole oxides and 6H-indeno[2,1-b]phosphindole 5-oxides for potential application in organic materials via sequential C(sp³)-H/C(sp²)-H functionalization. The method employs easily accessible starting materials and is endowed with high regioselectivity and broad functional-group tolerance.

Synthesis and characterisation of Pd(ii) and Au(i) complexes with mesoionic carbene ligands bearing phosphinoferrocene substituents and isomeric carbene moieites

While numerous functional ligands combining phosphine and imidazole-2-ylidene (or imidazolin-2-ylidene) donor moieties have already been reported, the chemistry of the corresponding functional mesoionic carbenes (MIC) derived from 1,2,3-triazoles remains nearly untapped. This contribution describes the synthesis of two isomeric series of triazolium salts bearing 1'-(diphenylphosphino)ferrocenyl substituents by [3 + 2] cycloaddition of a P-protected phosphinoferrocene alkyne with azides, or alternatively of a P-protected phosphinoferrocene azide with terminal alkynes, and by subsequent methylation. These salts were used to synthesize structurally unique Pd(ii) complexes featuring a P,C-chelating triazolylidene carbene ligands and Au(i)-MIC complexes with free phosphine groups. The latter were further utilised to prepare Pd(ii)Au(i) heterometallic complexes containing bridging ferrocene phosphino-carbenes as structurally flexible, donor-unsymmetric metalloligands. In addition, the reactivity of the newly prepared, P-protected phosphinoferrocene alkyne Ph₂PfcC[triple bond, length as m-dash]CH·BH₃ (fc = ferrocene-1,1'-diyl) was investigated, and representatives from all reported compound classes were structurally characterised.

Phosphindole fused pyrrolo[3,2-b]pyrroles: a new single-molecule junction for charge transport

A new family of phosphindole fused ladder-type heteroacenes with a pyrrolo[3,2-b]pyrrole core were synthesized and characterized, which show good luminescence efficiency, high thermostability and tunable conductance.

Photoredox-catalyzed decarboxylative alkylation/cyclization of alkynylphosphine oxides: a metal- and oxidant-free method for accessing benzo[b]phosphole oxides

By photoredox-catalysis, alkylation/aryl cyclization of alkynylphosphine oxides towards benzo[b]phospholes has been realized under metal- and oxidant-free conditions at room temperature.

Synthesis of 1,3-Azaphospholes with Pyrrolo[1,2- a]quinoline Skeleton and Their Optical Applications

A facile synthesis of 1,3-azaphospholes with a pyrrolo[1,2- a]quinoline skeleton has been described. These new annulated 1,3-azaphospholes exhibit good photoelectric performance and can be used as the emitting dopant in organic light-emitting diodes (OLEDs) and dye for bioimaging.

Regioselective functionalization at the 7-position of 1,2,3-triphenylbenzo[b]phosphole oxide via P[double bond, length as m-dash]O-directed lithiation

Various 7-substituted benzo[b]phosphole derivatives were prepared by P[double bond, length as m-dash]O-directed lithiation of 1,2,3-triphenylbenzo[b]phosphole P-oxide and subsequent iodination and cross-coupling reactions. The electron-donating groups introduced at the 7-position produced dramatic solvatofluorochromism owing to the strong charge-transfer character of the excited state of the entire π-system.

Supramolecular Assembly of Phosphole Oxide Based Alkynylplatinum(II) 2,6-Bis(N-alkylbenzimidazol-2'-yl)pyridine Complexes-An Interplay of Hydrophobicity and Aromatic π-Surfaces

A new class of phosphole oxide based alkynylplatinum(II) 2,6-bis(N-alkylbenzimidazol-2'-yl)pyridine (bzimpy) complexes were synthesized and characterized. Their self-assembly was driven by hydrophobic-hydrophobic and π-π stacking interactions. The self-assembly properties were also investigated by UV/Vis absorption spectroscopy, which revealed that the alkyl-chain length of the bzimpy moiety and the π-surface area of the alkynyl ligand have significant influence on the overall self-assembly process. The alkyl-chain length also affected the morphological structures of the aggregates, which were studied by transmission electron microscopy and scanning electron microscopy.

Synthesis of indole-fused heteroacenes by cascade cyclisation involving rhodium(ii)-catalysed intramolecular C–H amination

Indole-fused heteroacenes have been synthesised from cascade cyclisation of 2-[(2-azidophenyl)ethynyl]anilines and -phenols in a catalytic manner under redox-neutral conditions.

Synthesis and photophysical properties of novel benzophospholo[3,2-b]indole derivatives

The parent benzophospholo[3,2-b]indole was prepared by the reaction of dichlorophenylphosphine with a dilithium intermediate, which was prepared in two steps from 2-ethynyl-N,N-dimethylaniline. Using the obtained benzophosphole-fused indole as a common starting material, simple modifications were carried out at the phosphorus center of the phosphole, synthesizing various functionalized analogs. The X-ray structure analysis of trivalent phosphole and phosphine oxide showed that the fused tetracyclic moieties are planar. The benzophosphole-fused indoles, such as phosphine oxide, phospholium salt, and borane complex, exhibited strong photoluminescence in dichloromethane (Φ = 67–75%).

Versatile telluracycle synthesis via the sequential electrophilic telluration of C(sp2)-Zn and C(sp2)-H bonds

We report herein a new approach for the synthesis of tellurium-bridged aromatic compounds based on the sequential electrophilic telluration of C(sp2)-Zn and C(sp2)-H bonds with tellurium(iv) chlorides. A combination of transition metal-catalyzed (migratory) arylmetalation of alkynes and sequential telluration allows for the expedient construction of a library of functionalized benzo[b]tellurophenes. Furthermore, a variety of heteroarene-fused benzotellurophenes and other novel tellurium-embedded polycyclic aromatics can be readily synthesized from the corresponding 2-iodoheterobiaryls.

Direct Synthesis of Phospholyl Lithium from White Phosphorus

The selective construction of P-C bonds directly from P4 and nucleophiles is an ideal and step-economical approach to utilizing elemental P4 for the straightforward synthesis of organophosphorus compounds. In this work, a highly efficient one-pot reaction between P4 and 1,4-dilithio-1,3-butadienes was realized, which quantitatively affords phospholyl lithium derivatives. DFT calculations indicate that the mechanism is significantly different from that of the well-known stepwise cleavage of P-P bond in P4 activation. Instead, a cooperative nucleophilic attack of two Csp2 Li bonds on P4 , leading to simultaneous cleavage of two P-P bonds, is favorable. This mechanistic information offers a new view on the mechanism of P4 activation, as well as a reasonable explanation for the excellent yields and selectivity. This method could prove to be a useful route to P4 activation and the subsequent production of organophosphorus compounds.

Recent developments in synthetic methods for benzo[b]heteroles

Benzo[b]heteroles containing heteroatoms other than nitrogen and oxygen have received considerable attention for their potential applications in materials science. This poses an increasing demand for efficient, selective, and broad-scope methods for their synthesis. This review article summarizes the recent developments in synthetic methods and approaches to access representative members of the benzoheterole family.