Synthesis and Structure–Property Relationships of Phosphole‐Based π Systems and Their Applications in Organic Solar Cells

Phosphole is a chemically tunable heterole, and its π‐conjugated derivatives are potential candidates for optoelectronic materials. This account describes recent developments in the synthesis and structure–property relationships of π‐conjugated phosphole derivatives made by my research group. Thiophene–phosphole–styrene, phosphole–acetylene–arene, oligophosphole, polyphosphole, areno[c]phosphole, and phosphole–heterole π systems are synthesized using titanacycle‐mediated metathesis and palladium‐catalyzed cross‐coupling reactions. The structural, optical, and electrochemical properties of selected compounds are discussed. Initial results on some applications of thiophene–phosphole copolymers, acenaphtho[c]phospholes, and amine–terthiophene–phosphole donor–π–acceptor dyes in organic solar cells are described. These results give valuable information and guidelines for designing new phosphorus‐containing organic materials for molecular electronics.     

A Highly Modular One‐Pot Multicomponent Approach to Functionalized Benzo[b]phosphole Derivatives

Benzo[b]phosphole derivatives have attracted significant attention for their unique optoelectronic properties with potential for application in materials science. Herein we report a modular approach to a benzo[b]phosphole derivative based on a one‐pot sequential coupling of an arylzinc reagent, an alkyne, dichlorophenylphosphine (or phosphorus trichloride and a Grignard reagent), and an oxidant (for example H₂O₂, S, or Se). The approach allows for the construction of a library of previously inaccessible, structurally diverse benzo[b]phosphole derivatives with unprecedented ease.     

α,α′‐Diarylacenaphtho[1,2‐c]phosphole P‐Oxides: Divergent Synthesis and Application to Cathode Buffer Layers in Organic Photovoltaics

A divergent method for the synthesis of α,α′‐diarylacenaphtho[1,2‐c]phosphole P‐oxides has been established; α,α′‐dibromoacenaphtho[c]phosphole P‐oxide, which was prepared through a Ti^II‐mediated cyclization of 1,8‐bis(trimethylsilylethynyl)naphthalene, underwent a Stille coupling with three different kinds of aryltributylstannanes to afford the α,α′‐diarylacenaphtho[c]phosphole P‐oxides in moderate to good yields. X‐ray crystallographic analyses and UV/Vis absorption/fluorescence measurements have revealed that the degree of π‐conjugation, the packing motif, the electron‐accepting ability, and the thermal stability of the acenaphtho[c]phosphole π‐systems are finely tunable with the α‐aryl substituents. All the P?O and P?S derivatives exhibited high stability in their electrochemically reduced state. To use this class of arene‐fused phosphole π‐systems as n‐type semiconducting materials, we evaluated device performances of the bulk heterojunction organic photovoltaics (OPV) that consist of poly(3‐hexylthiophene), an indene‐C₇₀ bisadduct, and a cathode buffer layer. The insertion of the diarylacenaphtho[c]phosphole P‐oxides as the buffer layer was found to improve the power conversion efficiency of the polymer‐based OPV devices.     

金催化的炔烃羟基化反应: 合成2取代苯并呋喃化合物

本文报道了一种以邻炔基苯酚为原料,通过金催化的炔烃羟基化反应合成2取代苯并呋喃的方法. 该方法可以在温和的条件下快速以高产率得到各种2取代苯并呋喃. 关键前体邻炔基苯酚可以很容易由Sonogashira 反应制备.     

Highly Efficient and Diastereoselective Construction of Tricyclic Pyrrolidine‐Fused Benzo[b]thiophene 1,1‐dioxide Derivatives via 1,3‐Dipolar [3 + 2] Cycloaddition

A rapid and highly efficient 1,3‐dipolar [3 + 2] cycloaddition of nonstabilized azomethine ylides generated in situ with benzo[b]thiophene 1,1‐dioxides as the dipolarophiles has been developed. The efficient method affords tricyclic pyrrolidine‐fused benzo[b]thiophene 1,1‐dioxide derivatives in high to excellent yields (up to 99%) with excellent diastereoselectivities (up to >25:1 dr) under mild reaction conditions. The structure of a typical product was confirmed by X‐ray crystallography.     

Synthesis of new methylated thieno[2,3‐a] and [3,2‐b]carbazoles by reductive cyclization of 6‐(2′‐Nitrophenyl)benzo[b]thiophenes obtained by palladium‐catalyzed cross‐coupling isabel

The synthesis of new methylated thieno[2,3‐a] and [3,2‐b]carbazoles (5) (R=H) was achieved by a palladium‐catalyzed cross‐coupling, intramolecular reductive cyclization sequence of reactions. The cyclization precursors 6‐(2′‐nitrophenyl)benzo[b]thiophenes (3) were obtained by Suzuki cross‐coupling of 6‐boronated methylbenzo[b]thiophenes intermediates (2) with 2‐bromo or iodonitrobenzene. The boronated intermediates (2) were prepared via bromine‐lithium exchange followed by boron transmetalation and coupled in situ using Pd(OAc)₂ giving thus a “one‐pot” three steps reaction from the 6‐bromobenzo[b]thio‐phenes (1) to the cyclization precursors (3) . In the reductive cyclization step, N‐ethylthienocarbazoles (5) (R=Et) were also obtained. Several experiments have been made varying the amount of triethylphosphite and the time of reaction, to avoid their formation.     

Synthesis of Amphiphilic RuII Heteroleptic Complexes Based on Benzo[1,2‐b:4,5‐b′]dithiophene: Relevance of the Half‐Sandwich Complex Intermediate and Solvent Compatibility

The detailed synthesis and characterization of four ruthenium(II) complexes [RuLL′(NCS)₂] is reported, in which L represents a 2,2′‐bipyridine ligand functionalized at the 4,4′ positions with benzo[1,2‐b:4,5‐b′]dithiophene derivatives (BDT) and L′ is 2,2′‐bipyridine‐4,4′‐dicarboxylic acid unit (dcbpy) (NCS=isothiocyanate). The reaction conditions were adapted and optimized for the preparation of these amphiphilic complexes with a strong lipophilic character. The photovoltaic performances of these complexes were tested in TiO₂ dye‐sensitized solar cell (DSSC) achieving efficiencies in the range of 3–4.5 % under simulated one sun illumination (AM1.5G).     

2,2‐Bis(methoxy‐NNO‐azoxy)ethyl Derivatives of 4,8‐Dihydro‐bis‐furazano[3,4‐b:3′4′‐e]pyrazine: The Synthesis and X‐ray Investigation

The first synthesis of 4,8‐dihydro‐bis‐furazano[3,4‐b:3′4′‐e]pyrazine bearing 2,2‐bis(methoxy‐NNO‐azoxy)ethyl groups has been developed. These compounds are obtained by aza‐Michael reaction of 1,1‐bis(methoxy‐NNO‐azoxy)ethene or its equivalents, such as 2,2‐bis(methoxy‐NNO‐azoxy)ethanol derivatives, with 4,8‐dihydro‐bis‐furazano[3,4‐b:3′4′‐e]pyrazine.     

An Efficient Synthesis of Benzo[g]thiazolo[2,3‐b]quinazolin‐4‐ium and Benzo[g]benzo[4,5]thiazolo[2,3‐b]quinazolin‐14‐ium Hydroxides by a One‐pot,Three‐component Reaction under Green Conditions

A new series of benzo[g]thiazolo[2,3‐b]quinazolin‐4‐ium and benzo[g]benzo[4,5]thiazolo[2,3‐b]quinazolin‐14‐ium hydroxide derivatives have been synthesized by the one‐pot, three‐component reaction of aryl glyoxal monohydrates, 2‐hydroxy‐1,4‐naphthoquinone, and 2‐aminothiazole or 2‐aminobenzothiazole in the presence of triethylamine and p‐toluenesulfonic acid as organocatalysts in H₂O/acetone (2:1) at room temperature. This method offers mild reaction conditions, excellent yields, easy workup, and readily accessible starting materials and catalysts.     

Synthesis and functionalization of Poly[5,5′‐(silylene)‐2,2′‐dithienylene]s using silyl triflate intermediates†

Treatment of 5,5′‐dilithio‐2,2′‐dithiophene with (dimethylamino)methylsily bis(triflate)‐ or α, ω‐bis(triflate)‐substituted trisilanes gave poly[5,5′‐(silylene)‐2,2′‐dithienylene]s in high yields. The amino–silyl bond was cleaved selectively by triflic acid, leading to triflate‐substituted derivatives. Conversion of these compounds with nucleophiles gave other functionalized polymers. Platinum‐catalyzed hydrosilylation reactions between silicon–vinyl and silicon–hydrogen derivatives result in polymer networks which may serve as interesting preceramic materials. The structures of the polymers were proven by NMR spectroscopy (²⁹Si, ¹³C, ¹H). Results of thermal gravimetric analysis (TGA), UV spectrometry and conductivity measurements are given. Copyright © 1999 John Wiley & Sons, Ltd.     

[Au]/[Pd] Multicatalytic Processes: Direct One‐Pot Access to Benzo[c]chromenes and Benzo[b]furans

A new synthetic protocol that combines the advantages offered by eco‐friendly solvent‐free reactions and sequential transformations is reported. This strategy offers straightforward access to benzo[c]chromenes and benzo[b]furans from commercially available starting materials. This two‐step, one‐pot strategy consists of an Au‐catalyzed hydrophenoxylation process followed by Pd‐catalyzed C?H activation or Mizoroki–Heck reactions. The selectivity of the process towards C?H activation or Mizoroki–Heck reaction can be easily tuned.     

On the chemistry of 5‐aryl‐2‐hydrazino‐benzo[6,7]cyclohepta[1,2‐b]pyrido[2,3‐e] pyrimidin‐4‐one

Several pyrido[2,3‐e]pyrimidine fused with other rings have been prepared by intramolecular cyclization of 5‐(4‐chlorophenyl)‐2‐hydrazino‐benzo [6,7]cyclohepta‐[1,2‐b]pyrido[2,3‐e]pyrimidine‐4‐one ( 1 ) with acids, carbon disulfide to form triazole derivatives ( 2,4 ), halo‐ketones to give triazine derivative ( 5 ), β‐ketoesters, β‐cyanoesters, and β‐diketones to yield 2‐(1‐pyrazolyl) derivatives ( 7,9,10 ), and aldehydes to form arylhydrazone derivatives ( 11a,b ) which cyclized to form triazoles ( 12a,b ). Also, acyclic N‐nucleosides are prepared by heating under reflux 2‐hydrazino‐benzo[6,7]cyclohepta[1,2‐b]pyrido[2,3‐e] pyrimidin‐4‐one ( 1 ) with xylose and glucose to give the corresponding acyclic N‐nucleosides ( 13a,b ) which are cyclized to afford the corresponding protected tetra and penta–O‐acetate C‐nucleosides ( 14a,b ). Deacetylating of the latter nucleosides afforded the free acyclic C‐nucleosides ( 15a,b ). © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:34–43, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20248     

An Air‐Stable Semiconducting Polymer Containing Dithieno[3,2‐b:2′,3′‐d]arsole

Arsole‐containing conjugated polymers are a practically unexplored class of materials despite the high interest in their phosphole analogues. Herein we report the synthesis of the first dithieno[3,2‐b;2′,3′‐d]arsole derivative, and demonstrate that it is stable to ambient oxidation in its +3 oxidation state. A soluble copolymer is obtained by a palladium‐catalyzed Stille polymerization and demonstrated to be a p‐type semiconductor with promising hole mobility, which was evaluated by field‐effect transistor measurements.     

A Straightforward Route to Potent Phenolic Chain‐Breaking Antioxidants by Acid‐Promoted Transposition of 1,4‐Benzo[b]oxathiines to Dihydrobenzo[b]thiophenes

The transformation of simple phenols with limited antioxidant activity into potent chain‐breaking antioxidants was achieved by a three‐step protocol, consisting of the conversion of phenols into 1,4‐benzo[b]oxathiines followed by an unprecedented acid‐promoted transposition to o‐hydroxydihydrobenzo[b]thiophenes, or dihydrobenzo[de]thiochromenes, starting from phenols or naphthols, respectively. These derivatives, bearing a benzo‐fused heterocycle with a sulfide sulfur ortho to the phenolic OH, have a rate constant of reaction with alkylperoxyl radicals (k_inh) comparable to that of α‐tocopherol. A solid rationale for the transposition mechanism as well as for the structure‐antioxidant activity relationship is presented.     

Synthesis of novel pyrido[3′,2′:5,6]thiopyrano[3,2‐b]indol‐5(6H)‐ones and 6H‐pyrido[3′,2′:5,6]thiopyrano[4,3‐b]quinolines,two new heterocyclic ring systems

The synthesis of new pyrido[3′,2′:5,6]thiopyrano[3,2‐b]indol‐5(6H)‐ones was accomplished by the Fischer‐indole cyclization of some 2,3‐dihydro‐3‐phenylhydrazonothiopyrano[2,3‐b]pyridin‐4(4H)‐ones, obtained from the 2,3‐dihydro‐3‐hydroxymethylenethiopyrano[2,3‐b]pyridin‐4(4H)‐one, by the Japp‐Klingemann reaction. 6H‐Pyrido[3′,2′:5,6]thiopyrano[4,3‐b]quinolines were obtained by reaction of 2,3‐dihydrothiopyrano‐[2,3‐b]pyridin‐4(4H)‐ones with o‐aminobenzaldehyde or 5‐substituted isatins. The preparation of some derivatives, functionalized with an alkylamino‐substituted side chain, is also described.     

Diversity‐Oriented Synthesis of Substituted Benzo[b]thiophenes and Their Hetero‐Fused Analogues through Palladium‐Catalyzed Oxidative CH Functionalization/Intramolecular Arylthiolation

An efficient, high yielding route to multisubstituted benzo[b]thiophenes has been developed through palladium‐catalyzed intramolecular oxidative C?H functionalization–arylthiolation of enethiolate salts of α‐aryl‐β‐(het)aryl/alkyl‐β‐mercaptoacrylonitriles/acrylates or acrylophenones. The overall strategy involves a one‐pot, two‐step process in which enethiolate salts [generated in situ through base‐mediated condensation of substituted arylacetonitriles, deoxybenzoins, or arylacetates with (het)aryl (or alkyl) dithioates] are subjected to intramolecular C?H functionalization–arylthiolation under the influence of a palladium acetate (or palladium chloride)/cupric acetate catalytic system and tetrabutylammonium bromide as additive in N,N‐dimethylformamide (DMF) as solvent. In a few cases, the yields of benzo[b]thiophenes were better in a two‐step process by employing the corresponding enethiols as substrates. In a few examples, Pd(OAc)₂ (or PdCl₂) catalyst in the presence of oxygen was found to be more efficient than cupric acetate as reoxidant, furnishing benzothiophenes in improved yields by avoiding formation of side products. The method is compatible with a diverse range of substituents on the aryl ring as well as on the 2‐ and 3‐positions of the benzothiophene scaffold. The protocol could also be extended to the synthesis of a raloxifene precursor and a tubulin polymerization inhibitor in good yields. The versatility of this newly developed method was further demonstrated by elaborating it for the synthesis of substituted thieno‐fused heterocycles such as thieno[2,3‐b]thiophenes, thieno[2,3‐b]indoles, thieno[3,2‐c]pyrazole, and thieno[2,3‐b]pyridines in high yields. A probable mechanism involving intramolecular electrophilic arylthiolation via either a Pd‐S adduct or palladacycle intermediate has been proposed on the basis of experimental studies.     

An Efficient Synthesis of Pyrrolo[1,2‐a] or Pyrido[1,2‐a]benzo[4,5]imidazo[1,2‐c]quinazoline Derivatives in Ionic Liquids Catalyzed by Iodine

2‐(1H ‐benzo[d ]imidazol‐2‐yl)anilines reacted with haloketones including 5‐chloropentan‐2‐one and 6‐chlorohexan‐2‐one catalyzed by iodine, giving benzo[4,5]imidazo[1,2‐c ]pyrrolo[1,2‐a ]quinazoline and 6H ‐benzo[4,5]imidazo[1,2‐c ]pyrido[1,2‐a ]quinazoline derivatives, respectively. This domino‐type reaction formed two new heterocycles and three new covalent bonds in one‐pot procedure and provided a green method for the synthesis of fused pentacyclic heterocycles bearing both quinazoline and benzimidazole moieties in ionic liquids.     

Facile Assembly of Benzo[b]naphtho[2,3‐d]azocin‐6(5 H)‐ones by a Palladium‐Catalyzed Double Carbometalation

The palladium‐catalyzed reaction of 2‐alkynylanilines with 2‐(2‐bromobenzylidene)cyclobutanone as an efficient route to 7,8‐dihydrobenzo[b]naphtho[2,3‐d]azocin‐6(5 H)‐ones was developed. The fused eight‐membered ring was constructed conveniently. During the reaction process, double carbometalation was involved, which resulted in excellent selectivity with the formation of three new bonds. This transformation is highly efficient and leads to fused polycycles in good to excellent yields with good functional group tolerance.     

Assembly of π‐Conjugated Phosphole Azahelicene Derivatives into Chiral Coordination Complexes: An Experimental and Theoretical Study

Aza[n]helicene phosphole derivatives have been prepared from aza[n]helicene diynes by the Fagan–Nugent route. Their photophysical properties (UV/Vis absorption and emission behavior) have been evaluated. Their behavior as P,N chelates towards coordination to Pd^II and Cu^I has been investigated: metal–bis(aza[n]helicene phosphole) assemblies are formed by a highly stereoselective coordination process, as demonstrated by X‐ray crystallography. An aza[6]helicene phosphole bearing an enantiopure helicene part has been obtained, which allows the preparation of enantiopure Pd^II and Cu^I complexes with original topologies and high molar rotation (MR) and circular dichroism (CD). The structure–property relationship established from the experimental data has been studied in detail by theoretical studies (TDDFT calculations of UV/Vis, CD, and MR). Aza[n]helicene phosphole derivatives show π conjugation extended over the entire molecule, and its influence on the MR of aza[6]helicene phosphole 5 c has been demonstrated. Finally, it has been shown that the nature of the metal (coordination geometry and electronic interaction) can have a great impact on the amplitude of the chiroptical properties in metal–bis(aza[n]helicene phosphole) assemblies.     

Diversity‐Oriented Synthesis of Novel 2′‐Aminospiro[11H‐indeno[1,2‐b]quinoxaline‐11,4′‐[4H]pyran] Derivatives via a One‐Pot Four‐Component Reaction

A sequential one‐pot four‐component reaction for the efficient synthesis of novel 2′‐aminospiro[11H‐indeno[1,2‐b]quinoxaline‐11,4′‐[4H]pyran] derivatives 5 in the presence of AcONH₄ as a neutral, inexpensive, and dually activating catalyst is described (Scheme 1). The syntheses are achieved by reacting ninhydrin ( 1 ) with benzene‐1,2‐diamines 2 to give indenoquinoxalines, which are trapped in situ by malono derivatives 2 and various α‐methylenecarbonyl compounds 4 through cyclization, providing the multifunctionalized 2′‐aminospiro[11H‐indeno[1,2‐b]quinoxaline‐11,4′‐[4H]pyran] analogs 5 . This chemistry provides an efficient and promising synthetic way of proceeding for the diversity‐oriented construction of the spiro[indenoquinoxalino‐pyran] skeleton.