Vinyl Pyrrole Research Articles

Facile Preparation of Doxorubicin-Loaded and Folic Acid-Conjugated Carbon Nanotubes@Poly(N-vinyl pyrrole) for Targeted Synergistic Chemo–Photothermal Cancer Treatment

We developed a bifunctional nanoplatform for targeted synergistic chemo-photothermal cancer treatment. The nanoplatform was constructed through a facile method in which poly(N-vinyl pyrrole) (PVPy) was coated on cut multiwalled carbon nanotubes (c-MWNTs); FA-PEG-SH was then linked by thiol-ene click reaction to improve the active targeting ability, water dispersibility, and biocompatibility and to extend the circulation time in blood. The PVPy shell not only enhanced the photothermal effect of c-MWNTs significantly but also provided a surface that could tailor targeting molecules and drugs. The resulting MWNT@PVPy-S-PEG-FA possessed high drug-loading ratio as well as pH-sensitive unloading capacity for a broad-spectrum anticancer agent, doxorubicin. Owing to its outstanding efficiency in photothermal conversion and ability in targeted drug delivery, the material could potentially be used as an efficient chemo-photothermal therapeutic nanoagent to treat cancer.

Chemistry of aza- and diazafulvenium methides in heterocyclic synthesis

Abstract Aza- and diazafulvenium methide systems are versatile building blocks for the synthesis of pyrroles and pyrazoles. These extended dipoles participate in sigmatropic [1,8]H shifts and 1,7-electrocyclizations giving vinyl pyrroles and pyrazoles. Under flash vacuum pyrolysis conditions these heterocycles undergo interesting rearrangements. Aza- and diazafulvenium methides can be intercepted by dipolarophiles. Derivatives with carboxylate groups at C-4 and/or C-5 act exclusively as 1,7-dipoles affording products resulting from the addition across the 1,7-positions. These 1,7-cycloadducts include chlorin and bacteriochlorin type macrocycles as well as steroidal analogues, compounds with relevance in medicinal chemistry. In contrast with this chemical behavior, 5-trifluoromethylazafulvenium methides can participate in both 1,7- and 1,3-dipolar cycloadditions. The generation and reactivity of benzodiazafulvenium methides is also discussed.

Towards the Synthesis of Dihydrooxepino[4,3-b]pyrrole-Containing Natural Products via Cope Rearrangement of Vinyl Pyrrole Epoxides

An approach to the dihydrooxepino[4,3-b]pyrrole core of diketopiperazine natural products which utilizes a vinyl pyrrole epoxide Cope rearrangement was investigated. It was found that an ester substituent on the epoxide was essential for the [3,3]-rearrangement to occur. Density functional calculations with M06-2X provided explanations for the effects of the pyrrole and ester groups on these rearrangements.

Microwave-induced Pericyclic Reactions of Aza- and Diazafulvenium Methides

The pericyclic reactions of 4,5-dimethoxycarbonyl-substituted aza- and diazafulvenium methides generated under microwave-induced thermolysis conditions have been described. The 7,7-dimethyl-substituted derivatives undergo allowed suprafacial sigmatropic [1,8]-hydrogen shifts leading to the efficient synthesis of C-vinylpyrroles and Cvinylpyrazoles. These intermediates could not be trapped in [8Π+2Π] cycloaddition in the presence of dipolarophiles. Azaand diazafulvenium methides unsubstituted at C-1 and C-7 behave as 8Π 1,7-dipoles in the presence of dipolarophiles under microwave irradiation, leading to a range of pyrrolo and pyrazolo annulated heterocycles resulting from addition across positions 1 and 7. Aza- and diazafulvenium methide derivatives bearing only one methyl group at C-7 are intercepted in sigmatropic hydrogen shifts to give functionalized pyrroles and pyrazoles, respectively. In the presence of electron- deficient dipolarophiles, these 7-methyl-substituted derivatives act as 1,7-dipoles in [8Π+2Π] cycloadditions, however, competitive formation of the corresponding vinyl pyrroles and vinylpyrazoles is also observed.

Addition of Enamines or Pyrroles and B(C6F5)3 “Frustrated Lewis Pairs” to Alkynes

Reaction of 1-morpholinocyclohexene with B(C6F5)3 and phenylacetylene gave a mixture of two compounds, [C6H10N(CH2CH2)2O][PhCCB(C6F5)3] (1a) and C6H9(2-PhC═C(H)B(C6F5)3)(N(CH2CH2)2O (1b). The analogous reaction with ethynylferrocene resulted in only the deprotonation product, the alkynyl-borate salt [C6H10N(CH2CH2)2O][CpFe(C5H4)CCB(C6F5)3] (2). The related reactions of pyrrole, phenylacetylene, and B(C6F5)3 led to the vinyl-borate addition product, HNC4H4(2-PhC═C(H)B(C6F5)3) (3). In a similar fashion, reaction of N-methylpyrrole, phenylacetylene, and B(C6F5)3 gave a 3:2 ratio of the products MeNC4H4(2-PhC═C(H)B(C6F5)3) (4a) and MeNC4H4(3-PhC═C(H)B(C6F5)3) (4b), while the corresponding reaction of N-tert-butylpyrrole with phenylacetylene and B(C6F5)3 provided a single product, tBuNC4H4(3-PhC═C(H)B(C6F5)3) (5a). Variations in the aryl alkynes produced the corresponding addition complexes, tBuNC4H4(3-ArC═C(H)B(C6F5)3) (Ar = p-C6H4Br 5b, m-C6H4Cl 5c, p-C6H4CF3 5d, CpFe(C5H4) 5e). Similarly MeNC4H2(2,5-Me2)(3-ArC═C(H)B(C6F5)3) (Ar = Ph 6a, p-C6H4Br 6b, m-C6H4Cl 6c, p-C6H4CF3 6d, CpFe(C5H4) 6e) were derived from 1,2,5-trimethylpyrrole. The species 5a and 5b were shown to rearrange to give tBuNC4H3(3-ArC═C(H)(C6F5)B(C6F5)2) (Ar = Ph 7a, CpFe(C5H4) 7b). The related complexes RNC4H3(3-PhC═C(H)(C6F5)B(C6F5)2) (R = SiMe3 8, Ph 9) and MeNC4H(2,5-Me2)(3-PhC═C(H)(C6F5)B(C6F5)2) (10) were derived directly from the corresponding reactions of the pyrrole, PhCCH, and B(C6F5)3. In the case of the reaction of N-tert-butylpyrrole, phenylacetylene, and PhB(C6F5)2, phenyl group migration was observed, affording exclusively the species tBuNC4H3(3-PhC═C(H)(Ph)B(C6F5)2) (11). Reaction of 5a or 4a/4b and tBu3P resulted in deprotonation and formation of the salts [tBu3PH][RNC4H3(X-PhC═C(H)B(C6F5)3)] (R = tBu, X = 3 12; R = Me X = 2 13a, 3 13b). Reaction of 5a−d or 6a−d with one equivalent of Et3PO mediated proton transfer to generate a series of vinyl pyrroles tBuNC4H3(3-ArC═CH2) (Ar = Ph 14a, p-C6H4Br 14b, m-C6H4Cl 14c, p-C6H4CF3 14d) and MeNC4H2(2,5-Me2)(3-ArC═CH3) (Ar = Ph 15a, p-C6H4Br 15b, m-C6H4Cl 15c, p-C6H4CF3 15d) and the byproduct Et3PO·B(C6F5)3.

Investigations into the Parallel Synthesis of Novel Pyrrole-Oxazole Analogues of the Insecticide Pirate

Investigations into the parallel synthesis of selected analogues of a structurally unique pyrrole-oxazole analogue of the pyrrole insecticide pirate, are reported. Acylaminoketone salts were obtained from ketobromides in moderate to high yields and excellent purity. A number of N-tosyl pyrroles were obtained; however, formation of the target acyl tosyl pyrroles was thwarted by the stereoelectronic effects of the pyrrole substituents. During the pyrrole subunit chemistry, an interesting pyrrole derivative, vinyl pyrrole, was isolated. By restricting diversity to the aryl subunit, the parallel synthesis of selected pyrrole-oxazoles in moderate purity, was achieved when electron-donating or no groups were present on the aryl ring.

Palladium-Catalyzed Synthesis of N-Vinyl Pyrroles and Indoles

A stereospecific palladium-catalyzed N-vinylation of azaheterocycles with vinyl triflates is described. Cyclic and acyclic vinyl triflates along with nonnucleophilic azaheterocycles were found to be substrates for this palladium-catalyzed synthesis of N-vinyl pyrrole and indole derivatives.

Synthesis of Electric Conductive Poly(Arylene Vinylene) Containing Vinyl Pyrrole (PVP)

Abstract A new polyarylenevinylene containing vinyl pyrrole (PVP) was obtained from the monomer,2,5-bis(inethylenedimethylsulfo-niuin) chloride pyrrole, which was prepared from 2,5-dimethylpyrrole by the modified sulfonium polyelectrolyte precursor route. The polymerization conditions for the preparation of precursor polymers are described. The highest yield was obtained when the PYP was synthesized at-40°C with the monomer/base concentration ratios of 0.5/0.2 and thermally eliminated at 220°C. The electrical conductivity of the PVP synthesized with aforementioned conditions was given as 6.8 × 1O7 Scm−1.