Synthesis and Photovoltaic Properties of Cyclopentadithiophene‐Based Low‐Bandgap Copolymers That Contain Electron‐Withdrawing Thiazole Derivatives

We have synthesized four types of cyclopentadithiophene (CDT)‐based low‐bandgap copolymers, poly[{4,4‐bis(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene‐2,6‐diyl}‐alt‐(2,2′‐bithiazole‐5,5′‐diyl)] ( PehCDT‐BT ), poly[(4,4‐dioctyl‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene‐2,6‐diyl)‐alt‐(2,2′‐bithiazole‐5,5′‐diyl)] ( PocCDT‐BT ), poly[{4,4‐bis(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene‐2,6‐diyl}‐alt‐{2,5‐di(thiophen‐2‐yl)thiazolo[5,4‐d]thiazole‐5,5′‐diyl}] ( PehCDT‐TZ ), and poly[(4,4‐dioctyl‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene‐2,6‐diyl)‐alt‐{2,5‐di(thiophen‐2‐yl)thiazolo[5,4‐d]thiazole‐5,5′‐diyl}] ( PocCDT‐TZ ), for use in photovoltaic applications. The intramolecular charge‐transfer interaction between the electron‐sufficient CDT unit and electron‐deficient bithiazole (BT) or thiazolothiazole (TZ) units in the polymeric backbone induced a low bandgap and broad absorption that covered 300 nm to 700–800 nm. The optical bandgap was measured to be around 1.9 eV for PehCDT‐BT and PocCDT‐BT , and around 1.8 eV for PehCDT‐TZ and PocCDT‐TZ . Gel permeation chromatography showed that number‐average molecular weights ranged from 8000 to 14 000 g mol^?1. Field‐effect mobility measurements showed hole mobility of 10^?6–10^?4 cm² V^?1 s^?1 for the copolymers. The film morphology of the bulk heterojunction mixtures with [6,6]phenyl‐C₆₁‐butyric acid methyl ester (PCBM) was also examined by atomic force microscopy before and after heat treatment. When the polymers were blended with PCBM, PehCDT‐TZ exhibited the best performance with an open circuit voltage of 0.69 V, short‐circuit current of 7.14 mA cm^?2, and power conversion efficiency of 2.23 % under air mass (AM) 1.5 global (1.5 G) illumination conditions (100 mW cm^?2).     

Synthesis and characterization of new selenophene‐based conjugated polymers for organic photovoltaic cells

Three new polymers poly(3,4′′′‐didodecyl) hexaselenophene) (P6S), poly(5,5′‐bis(4,4′‐didodecyl‐2,2′‐biselenophene‐5‐yl)‐2,2′‐biselenophene) (HHP6S), and poly(5,5′‐bis(3′,4‐didodecyl‐2,2′‐biselenophene‐5‐yl)‐2,2′‐biselenophene) (TTP6S) that have the same selenophene‐based polymer backbone but different side chain patterns were designed and synthesized. The weight‐averaged molecular weights (M_w) of P6S, HHP6S, and TTP6S were found to be 19,100, 24,100, and 19,700 with polydispersity indices of 2.77, 1.48, and 1.41, respectively. The UV–visible absorption maxima of P6S, HHP6S, and TTP6S are at 524, 489, and 513 nm, respectively, in solution and at 569, 517, and 606 nm, respectively, in the film state. The polymers P6S, HHP6S, and TTP6S exhibit low band gaps of 1.74, 1.95, and 1.58 eV, respectively. The field‐effect mobilities of P6S, HHP6S, and TTP6S were measured to be 1.3 × 10^?4, 3.9 × 10^?6, and 3.2 × 10^?4 cm² V^?1 s^?1, respectively. A photovoltaic device with a TTP6S/[6,6]‐phenyl C₇₁‐butyric acid methyl ester (1:3, w/w) blend film active layer was found to exhibit an open circuit voltage (V_OC) of 0.71 V, a short circuit current (J_SC) of 5.72 mA cm^?2, a fill factor of 0.41, and a power conversion efficiency (PCE) of 1.67% under AM 1.5 G (100 mW cm^?2) illumination. TTP6S has the most planar backbone of the tested polymers, which results in strong π–π interchain interactions and strong aggregation, leading to broad absorption, high mobility, a low band gap, and the highest PCE. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and properties of the conjugated polymers with indenoindene and benzimidazole units for organic photovoltaics

A new electron deficient unit, dimethyl‐2H‐benzimidazole (MBI), and dihydroindeno[2,1‐a]indene (ININE) moiety as electron‐rich unit were coupled to synthesize the conjugated polymers containing electron donor–acceptor pair for organic photovoltaics. ININE, MBI, and thiophene (or bithiophene) units were incorporated using Stille and Suzuki polymerization to generate poly(2,7‐(5,5,10,10‐tetrakis(2‐ethylhexyl)‐5,10‐dihydro‐ indeno[2,1‐a]indene)‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2,2‐dimethyl‐2H‐benzimidazole)) (PININEDTMBIs) (or PININEBBTMBIs). In MBI, the sulfur at 2‐position of 2,1,3‐benzothiadiazole (BT) unit was replaced with dialkyl‐substituted carbon, whereas keeping the 1,2‐quinoid form, to improve the solubility of the polymers. The field‐effect hole mobility of PININEBBTMBI was 3.2 × 10^?4 cm²/Vs which was improved as compared to that of PININEDTMBI (2.7 × 10^?5 cm²/Vs) caused by the introduction of bithiophene units. In case of the most efficient polymer, PININEBBTMBI, the device with the configuration of indium tin oxide (ITO)/poly(3,4‐ethylenedioxythiophene) (PEDOT):polystyrene sulfonate (PSS)/polymer:PC₇₁BM(1:4 w/w)/Al, annealed at 100 °C for 10 min demonstrated a open circuit voltage of 0.78 V, a short‐circuit current density of 6.66 mA/cm², and a fill factor of 0.41, leading to the power conversion efficiency of 2.11%, under white‐light illumination (AM 1.5 G, 100 mW/cm²). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Nitration of dithieno[3,2-b:3′,2′-d]pyridine and dithieno[3,2-b:3′,4′-d]pyridine

Nitration of dithieno[3,2-b:3′,2′-d]pyridine ( 4 ) and dithieno[3,2-b:3′,4′-d]pyridine ( 5 ) has been studied. Nitration of 4 occurred in both positions of the C ring, while 5 was predominantly substituted on the 3,4-fused ring. The structures of the nitro derivatives were proven by extensive use of ¹H and ¹³C nmr spectroscopy.     

Modulation of electronic properties of π‐conjugated copolymers derived from naphtho[1,2‐b:5,6‐b′]dithiophene donor unit: A structure‐property relationship study

A set of three donor‐acceptor conjugated (D‐A) copolymers were designed and synthesized via Stille cross‐coupling reactions with the aim of modulating the optical and electronic properties of a newly emerged naphtho[1,2‐b:5,6‐b′]dithiophene donor unit for polymer solar cell (PSCs) applications. The PTNDTT‐BT , PTNDTT‐BTz , and PTNDTT‐DPP polymers incorporated naphtho[1,2‐b:5,6‐b′]dithiophene ( NDT ) as the donor and 2,2′‐bithiazole ( BTz ), benzo[1,2,5]thiadiazole ( BT ), and pyrrolo[3,4‐c]pyrrole‐1,4(2H,5H)‐dione ( DPP ), as the acceptor units. A number of experimental techniques such as differential scanning calorimetry, thermogravimetry, UV–vis absorption spectroscopy, cyclic voltammetry, X‐ray diffraction, and atomic force microscopy were used to determine the thermal, optical, electrochemical, and morphological properties of the copolymers. By introducing acceptors of varying electron withdrawing strengths, the optical band gaps of these copolymers were effectively tuned between 1.58 and 1.9 eV and their HOMO and LUMO energy levels were varied between ?5.14 to ?5.26 eV and ?3.13 to ?3.5 eV, respectively. The spin‐coated polymer thin film exhibited p‐channel field‐effect transistor properties with hole mobilities of 2.73 × 10^?3 to 7.9 × 10^?5 cm² V^?1 s^?1. Initial bulk‐heterojunction PSCs fabricated using the copolymers as electron donor materials and [6,6]‐phenyl C71 butyric acid methyl ester (PC₇₁BM) as the acceptor resulted in power conversion efficiencies in the range of 0.67–1.67%. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2948–2958     

New Polymers for Optimizing Organic Photovoltaic Cell Performances

The performance of an organic solar cell critically depends on the materials used in the active layer. Desirable characteristics of active layer materials include an intense optical absorption covering broad range of the solar spectrum to maximize photon capture, the ability to effectively separate charges upon photo‐excitation, high charge mobility to allow efficient charge transport to the electrodes, and suitable HOMO and LUMO levels to ensure a high device voltage. In order to optimize these properties simultaneously, we have designed and synthesized conjugated polymers containing alternating electron‐donating and electron‐accepting units. Based on one of the low band gap polymers we designed and synthesized previously, poly[2,6‐(4,4‐bis‐(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene)‐alt‐4,7‐(2,1,3‐benzothiadiazole)], we carried out both side chain and main chain modifications in order to improve performance even further. By incorporating fluorene repeating units into the main chain, it is possible to adjust the absorption characteristics of the polymers while maintaining a desirable HOMO level and good charge carrier mobility. The solubility profile of the polymer can be adjusted by modifying the side chains, and soluble polymer with mobility as high as 7×10^?2 cm²/Vs is realized when a combination of 2‐ethylhexy and hexyl groups are used as side chains. These polymers should be promising candidates for high performance solar cells according to a recently published model (3).     

Anthradithiophene–thiophene copolymers with broad UV–vis absorption for organic solar cells and field‐effect transistors

New semiconducting copolymers, poly((TIPS‐ADT)‐(4,4′‐didodecyl‐2,2′‐bithiophene)) (PTADT2) and poly((TIPS‐ADT)‐(2,2′‐(4,4′‐didodecyl‐2,2′‐bithiophene)dithiophene)) (PTADT4) , produced by incorporating 5,11‐bis(triisopropylsilylethynyl) anthra[2,3‐b:7,6‐b']dithiophene (TIPS‐ADT) and alkyl‐thiophene derivatives were synthesized via Stille coupling polymerization. The optical, electrochemical, structural, field‐effect transistor, and solar cell properties of the polymers were investigated. The polymers showed good solubility at room temperature in common organic solvents due to their abundant side groups including TIPS and dodecyl side chains. Both polymers showed very broad UV absorption spectra covering the spectral range from 300 to 750 nm as a result of the combination of the different absorption ranges of the TIPS‐ADT unit (short wavelength region) and thiophene derivatives (long wavelength region). The FET device fabricated using PTADT4 containing additional unsubstituted thiophene rings as a spacer between TIPS‐ADT and thiophene derivatives showed a higher hole mobility (5.7 × 10^?4 cm²/V s) than the PTADT2 device (2.8 × 10^?5 cm²/V s), due to the improved intermolecular ordering caused by the reduced steric hindrance between bulky side chain groups. In addition, the PTADT4 :(6,6)‐phenyl‐C₇₀‐butyric acid methyl ester (PC₇₀BM) device showed an enhanced power conversion efficiency (PCE) of 1.30% compared with the PTADT2 :PC₇₀BM device (PCE of 0.55%) under AM 1.5G irradiation (100 mW/cm²). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Direct bromination of dithieno[3,4-b:3′,4′-d]pyridine and dithieno[2,3-b:3′,2′-d]pyridine

Bromination of dithieno[3,4-b:3′,4′-d]pyridine ( 1 ) and dithieno[2,3-b:3′,2′-d]pyridine ( 2 ) has been studied. Disubstitution occurred at both positions of the C ring. The substitution pattern is found to be similar to that of the nitration reaction. The structures of bromo derivatives were established by ¹H and ¹³C nmr spectroscopy.     

Structure-property relationships of benzo[2,1-b:3,4-b’]bis[1]benzothiophenes for organic field effect transistors

A series of novel benzo[2,1-b:3,4-b’]bis[1]-benzothiophene (BBBT) derivatives with different side-chains were synthesized and characterized. And their mobility properties were evaluated based on their active layers in OFETs devices. By means of simple thermal annealing, the devices based on BBBT-4 and BBBT-6 exhibited typical p-type FETs behavior with average hole mobilities of 0.28 and 0.124?cm² V^?1?s^?1, respectively. Furthermore, the structure-property relationships of these semiconductors were also investigated by XRD and AFM.     

Polymeric amines and their copper(II) complexes: Catalysts for the hydrolysis of organophosphate esters

Catalysis of the solvolysis of organophosphorus esters by polymers of aliphatic amines, imidazole, pyridine, 2,2′-bipyridine, and their copper(II) complexes was studied using diisopropyl fluorophosphate (DEP) as a model substrate. The polymeric catalysts were synthesized either by (1) derivation of available polymers, including polyethylenimine, polyvinyl amine, polyvinyl alcohol, polystyrene, and poly-4-vinylpyridine or (2) by polymerization of functionalized monomers such as 4(5)-vinylimidazole and 4-vinyl-4′-methyl-2,2′-bipyridine. Polymer hydrophilicity was controlled by partial quaternization of amine groups with different alkyl halides. The greatest catalytic activity was exhibited by copper(II) complexes of polymers containing the 2,2′-bipyridine group. At pH 7.6 and 3.7 × 10^?3M, the most active of these catalysts reduced the half-life of DFP from 800 to 9 min. The rate was largely independent of the pH in the range 6.5–8.5 but was limited by the aqueous solubility of the catalyst. Heterogeneous catalysis by some polymers was observed but was less effective. A Lineweaver-Burk plot of V₀^?1 versus [DFP]^?1 for a soluble polymeric 2,2′-bipyridine-copper(II) catalyst was linear. There was no correlation between catalysis of solvolysis of DFP and the carboxylic ester, p-nitrophenyl acetate.     

Synthesis of 1,6-didecylnaphtho[1,2-b:5,6-b']difuran-based copolymers by direct heteroarylation polymerization

The use of direct C H arylation cross-coupling polymerization was evaluated for the synthesis of donor–acceptor conjugated co-polymers using the novel donor 1,6-didecylnaphtho[1,2-b:5,6-b']difuran and either thieno[3,4-c]pyrrole-4,6-dione (TPD) or 1,4-diketopyrrolo[3,4-c]pyrrole (DPP) as the acceptor. Thiophene and furan moieties were used to flank the DPP group and the impact of these heterocycles on the polymers' properties was evaluated. The alkyl chains on the diketopyrrolopyrrole monomers were varied to engineer the solubility and morphology of the materials. All of the polymers have similar optoelectronic properties with narrow optical band gaps around 1.3 eV, which is ideal for solar energy harvesting. Unfortunately, these polymers also had high-lying highest occupied molecular orbital levels of −4.8 to −5.1, and as a result bulk-heterojunction photovoltaic cells fabricated using the soluble fullerene derivative PC₇₁BM as the electron-acceptor and these polymers as donor materials exhibited poor performance due to limited V_oc values. An examination of the films from these blends indicates that film-thickness and morphology were also a major hindrance to performance and a potential point of improvement for future materials.     

Reaction of 2,2′-bis(N-methylindolyl) with dimethyl acetylenedicarboxylate and thermally- and photochemically-induced cyclizations of the product

2,2′-Bis(N-methylindolyl) 1 reacts with dimethyl acetylenedicarboxylate to furnish the 3-dimethyl maleoyl-substituted 2,2′-bisindolyl 2 . Compound 2 cyclizes under aluminum trichloride catalysis according to a polar process to give a cyclopenta[2,1-b:3,4-b′]diindole derivative 4 . Reaction of compound 4 with benzyl-amine yields the spiro derivative 5 . Photochemically-induced 1,6-electrocyclization of compound 2 gives rise to the indolo[2,3-a]carbazole 6 directly, which is readily transformed to the pyrrolo-annelated carbazole 7 by treatment with benzylamine.     

Nitration of dithieno[3,4-b:3′,2′-d]pyridine and dithieno[2,3-b:3′,2′-d]pyridine

The nitration of dithieno[3,4-b:3′,2′-d]pyridine ( 2 ) and dithieno[2,3-b:3′,2′-d]pyridine ( 3 ) has been studied. Nitration of 2 occurred in both positions of the c-fused thiophene ring, while 3 was predominantly substituted in the 2-position. The structures of the nitro derivatives were proven by extensive use of ¹H and ¹³C nmr spectroscopy.     

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.     

Synthesis and characterization of isoindigo‐based polymers using CH‐arylation polycondensation reactions for organic photovoltaics

A series of three new low bandgap donor–acceptor–donor–acceptor^/ (D–A–D–A^/) polymers have been successfully synthesized based on the combination of isoindigo as the electron‐deficient acceptor and 3,4‐ethylenedioxythiophene as the electron‐rich donor, followed by CH‐arylation with different acceptors (4,7‐dibromo[c][1,2,5]‐(oxa, thia, and/or selena)diazole ( 4a‐c )). These polymers were used as donor materials for photovoltaic applications. All of the polymers are highly stable and show good solubility in chlorinated solvents. The highest power conversion efficiency of 1.6% was achieved in the bulk heterojunction photovoltaic device that consisted of poly ((E)?6‐(7‐(benzo‐[c][1,2,5]‐thiadiazol‐4‐yl)?2,3‐dihydrothieno‐[3,4‐b][1,4]dioxin‐5‐yl)?6′‐(2,3‐dihydrothieno‐[3,4‐b][1,4]‐dioxin‐5‐yl)?1,1′‐bis‐(2‐octyldodecyl)‐[3,3′‐biindolinylidene]‐2,2′‐dione) as the donor and PC₆₁BM as the acceptor, with a short‐circuit current density (J_sc) of 8.10 mA/cm², an open circuit voltage (V_oc) of 0.56 V and a fill factor of 35%, which indicates that these polymers are promising donors for polymer solar cell applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2926–2933     

High fluorescent ethyl acrylate modified PEDOT‐MeNH2 with enhanced electrochromic performance

Two poly(2'‐aminomethyl‐3,4‐ethylenedioxythienylene) (PEDOT‐MeNH₂) derivatives were successfully synthesized by electrochemical polymerization of precursors, diethyl 3'‐(((2,3‐dihydrothieno[3,4‐b][1,4]dioxin‐2‐yl) methyl)azanediyl)dipropanoate ( monomer 1 ) and ethyl 3‐(((2,3‐dihydrothieno[3,4‐b][1,4]dioxin‐2‐yl) methyl)amino)propanoate ( monomer 2 ), respectively. Structure–property relationships of monomers and polymers, including electrochemical, optical properties, and morphology, were systematically explored. Significantly, the designed polymers exhibited red and orange emission signatures with high fluorescence quantum yields (Φ_F) of 0.044 and 0.045 compared with those of monomers; they may be used as building blocks for rational design of fluorescent materials. Moreover, cyclic voltammetry and spectroelectrochemistry studies demonstrated that poly(diethyl 3'‐(((2,3‐dihydrothieno[3,4‐b][1,4]dioxin‐2‐yl)methyl)azanediyl) dipropanoate) ( P1 ) and poly(ethyl 3‐(((2,3‐dihydrothieno[3,4‐b][1,4]dioxin‐2‐yl)methyl)amino) propanoate) ( P2 ) can be reversibly oxidized and reduced accompanied by obvious color changes from light purple to light blue for P1 , and from purple to blue for P2 . Furthermore, both P1 and P2 displayed higher optical contrasts (40–70%) in the visible region, favorable coloration efficiency (typically 50–230 cm² C^?1). From these results, the two polymers would be promising candidate materials for display applications. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2081–2091     

Some mixed-ligand palladium(II) complexes and comparison of their photosensitizing ability with analogous platinum(II) complexes

Three new palladium(II) complexes of formula [Pd(bipy)(XX)] [where bipy is 2,2′-bipyridine and XX are dianions of catechol (CAT), 4-tert-butylcatechol (BCAT) and 3,4-dimercaptotoluene (DMT)] have been prepared and characterized by physical methods. A ligand-ligand charge-transfer band in each complex was observed between 16–21 kK (ε_max = 1500–2200 1 mol^?1 cm^?1) which is negatively solvochromic. These palladium(II) complexes in dimethylformamide photosensitize the formation of singlet oxygen and their ability to photosensitize triplet oxygen (³O₂) to singlet oxygen (¹O₂) are compared with analogous platinum(II) complexes. In addition, 2,2′-bipyridine-platinum(II) complex of 3,4-dimercaptotoluene also undergoes self-sensitized photooxidation.     

Donor–acceptor‐structured naphtodithiophene‐based copolymers for organic thin‐film transistors

New donor–acceptor (D‐A) polymers, poly(4,5‐bis(2‐octyldodecyloxy)naphto[2,1‐b:3,4‐b']dithiophenebenzo[c][1,2,5]thiadiazole) (PNDT‐B) and poly(4,5‐bis(2‐octyldodecyloxy)naphto [2,1‐b:3,4‐b′]dithiophene‐4,7‐di(thiophen‐2‐yl)benzo[c][1,2,5]thiadiazole) (PNDT‐TBT), with the extended π‐electron delocalization of naphtho[2,1‐b:3,4‐b']dithiophene, were successfully synthesized by Suzuki and Stille coupling reactions. The structure and physical properties of polymers were characterized by DFT calculation, UV–vis absorption, cyclovoltammetry, TGA and DSC analyses. X‐ray diffraction studies indicated a relatively highly ordered intermolecular structure in PNDT‐TBT after annealing. This high degree of molecular order resulted from the crystallinity and increasing planarity, provided by the thiophene linker groups and the interdigitation of the long alkoxy side chains. The new D‐A polymer, PNDT‐TBT, exhibited a p‐type carrier mobility of 0.028 cm²/Vs and an on/off ratio of 5.9 × 10³. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 525–531     

Synthesis and photovoltaic properties of a star-shaped molecule based on a triphenylamine core and branched terthiophene end groups

A new star-shaped donor-acceptor molecule has been synthesized for application as the donor material in solution-processed bulk-heterojunction organic solar cells (OSCs). The molecule consists of a triphenylamine (TPA) unit as the core and a donor unit with three arms containing benzo[1,2,5]thiadiazole (BT) acceptor units and 5,5’’-dihexyl-2,2′:3′,2″-terthiophene (tTh) end groups. The molecule, denoted S(TPA-BT-tTh), exhibits a broad absorption band in the wavelength range 300-650 nm and high hole mobility of 1.1×10 -4 cm2 V -1 s 1 . An OSC device based on S(TPA-BT-tTh) as donor and [6,6]-phenyl C71 -butyric acid methyl ester (PC 70 BM) as the acceptor (1:3, w/w) exhibited a power conversion efficiency of 2.28% with a short circuit current density of 6.39 mA/cm2 under illumination of AM.1.5, 100 mW/cm2 .     

Nitrogen bridgehead compounds. Part 86. Synthesis and reactivity of 7,12-dihydropyrimido[1′,2′;1,2]pyrido[3,4-b]indol-4(6H)-ones. Debenzologues of rutaecarpine alkaloids

A series of 7,12-dihydropyrimido[1′2′:1,2]pyrido[3,4-b]mdole-4(6H)-ones was prepared by Fischer indolization of 9-arylhydrazono-6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrirmdin-4-ones. Quantum chemical calculations (ab initio and AM1) indicate that position 3 of 7,12-dihydropyrimido[1′,2′:1,2]pyrido-[3,4-b]indole-4(6H)-one can be involved in electrophilic substitutions, while position 2 is sensitive towards nucleophilic attack. Bromination of 6-methyl-7,12-tetrahydropyrimido[1′,2′:1,2]pyrido-[3,4-b]indol-4(6H)-one 16 with bromine afforded 3-bromo derivative 25 , which was reacted with cyclic amines to give 2-ammo-7,12-dihydropyrirmdo[1′2′:1,2]pyrido[3,4-b]indol-4(6H)-ones 26–30 in an addition-elimination reaction. Vielsmeier-Haack formylation of compound 16 gave 12-formyl 31 and 3,12-diformyl 32 derivatives (an N-formyl-1-deaza derivative of nauclefidine alkaloid 34 ) at 60° and 100°, respectively. 3,12-Diformyl compound 32 was oxidized to 3-carboxyl derivative 33 with potassium permanganate. The quaternary salt 35 , obtained from compound 16 with dimethyl sulfate, suffered a ring opening on the action of aqueous sodium hydroxide. The new compounds have been characterized by elemental analyses uv, ¹H nmr and in some cases by ¹³C ruler, CD spectra and X-ray investigations.