Synthesis of new fluorescent building blocks via the microwave-assisted annulation reaction of 1,1,2-trimethyl-1H-benzo[e]indole with acrylic acid and its derivatives

The reaction of 1,1,2-trimethyl-1H-benzo[e]indole with acrylic acid and its derivatives was employed for the preparation of novel fluorescent building blocks. Treatment of 1,1,2-trimethyl-1H-benzo[e]indole with acrylic acid, acrylamide or tert-butyl acrylate in an autoclave or a microwave reactor at 180–200 °C afforded benzo[e]pyrido[1,2-a]indole derivatives. Various chemical transformations of the latter compounds have been performed to yield functionalized benzo[e]indole scaffolds. The structure assignments were based on data from ¹H and ¹³C NMR spectroscopy and single crystal X-ray analyses. The optical properties of the obtained benzo[e]indoline derivatives were studied by UV–vis and fluorescence spectroscopy.     

Total synthesis of the indole alkaloids henrycinol A and B

The total synthesis of new indole alkaloids henrycinol A and B were accomplished starting from l-tryptophan methyl ester. The key step is a stereochemically flexible Pictet–Spengler reaction governed by the presence or absence of an N-allyl group in the tryptophan precursor. The natural products henrycinol A and B were synthesized in good overall yield in eight and nine steps, respectively.     

Indole alkaloids from cultivated Vinca major

Nine new indole alkaloids, vinmajines A–I (1–9), and 43 known indole alkaloids were isolated from cultivated Vinca major in Kunming. The new structures were elucidated by extensive spectroscopic and quantum theory analysis. In addition, the results also supported that types of indole alkaloids from V. major might be influenced significantly by the ecological environment.     

Synthesis of hexahydroisoindole-3a-carboxylates by IMDA reaction of Morita–Baylis–Hillman adduct-derived dienes bearing a Z-alkenyl tether

An intramolecular Diels–Alder (IMDA) reaction of Morita–Baylis–Hillman adduct-derived dienes bearing a Z-alkenyl dienophile tether afforded hexahydroisoindole-3a-carboxylates in excellent yields and stereoselectivity.     

A concise synthesis of novel naphtho[a]carbazoles and benzo[c]carbazoles

Starting from simple indole precursors the synthesis of naphtho[a]carbazoles and benzo[c]carbazoles is described. Key steps include the use of the Suzuki-Miyaura reaction to afford 2- or 3-aryl substituted indoles, as well as a potassium t-butoxide and light assisted aromatic ring-forming reaction.     

Organocatalytic asymmetric Friedel–Crafts reaction of 1-naphthols with isatins: an enantioselective synthesis of 3-aryl-3-hydroxy-2-oxindoles

An organocatalytic enantioselective Friedel–Crafts reaction of 1-naphthols with isatins has been developed employing bifunctional thiourea–tertiary amine organocatalysts. A variety of isatin derivatives react well with 1-naphthols in the presence of Cinchona derived thiourea 1a to provide biologically important chiral 3-aryl-3-hydroxy-2-oxindoles (3a–zg) in good yield (70–84%) and moderate to good enantioselectivity (37–83%).     

A simple,efficient, regioselective and one-pot preparation of N-hydroxy- and N–O-protected hydroxyindoles via cycloaddition of nitrosoarenes with alkynes. Synthetic scope,applications and novel by-products

The thermal reaction between nitrosoarenes and alkynes under alkylating conditions produces N-alkoxyindoles as the major products in moderate to good yields and excellent regioselectivity. Various electrophiles are used affording different N–O-protected hydroxyindoles in a multi-component fashion. Privileged acetylenic substrates used in reactions with substituted nitrosoarenes are arylalkynes or propiolates. Potentially bioactive compounds and other classes of highly functionalizable indole products were prepared. Reactions between o-carbomethoxy-nitrosoarenes and arylacetylenes provided tricyclic compounds containing an acylaziridine indoline skeleton.     

The Diels–Alder reactions of para-benzoquinone nitrogen-derivatives: an experimental and theoretical study

An experimental and theoretical study of the comparative reactivity and selectivity of the Diels–Alder reactions of para-benzoquinones and three nitrogen derivatives have been performed. The mono-oximes derivatives do not react under the tested reaction conditions, whereas the tosylated mono-oximes react slowly. However, the mono N-tosyl imines show excellent reactivity, and superior to the parent para-benzoquinones. DFT calculations support these experimental results.     

Mild method for the synthesis of 1H-indazoles through oxime-phosphonium ion intermediate

The synthesis of 1H-indazoles from o-aminobenzoximes is achieved via N–N bond formation using triphenylphosphine, I₂, and imidazole. Selective formation of oxime-phosphonium ion intermediate in the presence of the amino group is the driving force for this reaction. The nucleophilicity of the arylamino group and electrophilicity toward the N–O bond of oxime also control the reaction. The reaction proceeds at a faster rate with good to excellent yield under this mild reaction condition and is amenable to scale-up.     

Synthesis of a novel tricyclic 1,6,7,8-tetrahydro-2H-cyclopenta[b]furo[3,2-d]pyridine derivative,the 5-aza analog of ramelteon

The 5-aza analog of ramelteon 3, a novel tricyclic 1,6,7,8-tetrahydro-2H-cyclopenta[b]furo[3,2-d]pyridine derivative, was synthesized by hetero-Diels–Alder reaction and chemoselective Dieckmann condensation.     

Systematic study for the stereochemistry of the Atherton–Todd reaction

Under the Atherton–Todd reaction conditions, the stereochemistry on the reaction of H-phosphinates with different nucleophiles (e.g., amines, alcohols, phenols) was investigated. All reactions took place stereospecifically with inversion of configurations at the phosphorus centers. The reaction might proceed via a phosphoryl chloride intermediate with retention of configuration at phosphorus, followed by the attack of nucleophiles from the backside of Cl to give the substitution products with inversion of configuration at the phosphorus center. A plausible mechanism was proposed for these reactions.     

Stereoselective total synthesis of ieodomycin C

A concise stereoselective synthesis of the marine natural product ieodomycin C (3) has been achieved from commercially available pyridinium-1-sulfonate (8) in eight linear steps and 14% overall yield. The key synthetic steps included a B-alkyl Suzuki–Miyaura cross-coupling reaction and an Evans–Nagao acetate aldol reaction. The same synthetic sequence was used for preparing the enantiomer of ieodomycin C (3). Our efforts confirmed the structure of the antibacterial natural product 3.     

Hyrtimomines,indole alkaloids from Okinawan marine sponges Hyrtios spp.

Six new indole alkaloids, hyrtimomines F–K (1–6), were isolated from Okinawan marine sponges Hyrtios spp. The structures of 1–6 were elucidated on the basis of spectroscopic analysis. Hyrtimomine F (1) is a structurally unique bisindole alkaloid possessing an α-keto-?-caprolactam ring, while hyrtimomine G (2) is a symmetrical bisindole alkaloid. Hyrtimomines H–K (3–6) are indole alkaloids possessing β-carboline skeleton with an imidazolium unit. Antimicrobial activities of hyrtimomines F–K (1–6) were evaluated.     

Facile intramolecular Diels–Alder reaction of 4-(o-propargyloxy)styrylcoumarins leading to highly fluorescent coumarin-containing polycyclic compounds

The 4-(o-propargyloxy)styrylcoumarins are prepared by the condensation of O-propargylated salicylaldehyde with substituted coumarin-4-acetic acids. The intramolecular Diels–Alder reaction of 4-(o-propargyloxy)styrylcoumarins, without any catalyst gives fused-ring coumarins. The reaction in boiling nitrobenzene leads to aromatization of the initial Diels–Alder adduct and these aromatized products are highly fluorescent.     

Solvent-dependent Baylis–Hillman reactions for the synthesis of 3-benzyl-3-hydroxyoxindoles and benzo-δ-sultams

We have developed a solvent-dependent method for the preparation of novel benzo-δ-sultam and 3-benzyl-3-hydroxy-N-methyloxindole scaffolds. A variety of 3-(methoxy(phenyl)methyl)-1-methyl-1H-benzo-[c][1,2]thiazine 2,2-dioxides and 3-benzyl-3-hydroxy-1-methylindolin-2-ones were obtained in moderate to high yields via DBU-catalyzed Baylis–Hillman reaction of a number of (E)-N-(2-formylphenyl)-N-methyl-2-phenylethenesulfonamides in DMF and MeOH, respectively. The proof of the structures relies on analytical investigation and X-ray crystallography. Whereas reaction of (E)-N-(2-formylphenyl)-N-methyl-2-phenylethenesulfonamides in MeOH presumably proceeds through intramolecular Baylis–Hillman/dehydration, 3-hydroxy-N-methyloxindoles seem to have been generated via intramolecular Baylis–Hillman/1,3-H shift/oxidation/intramolecular cyclization tandem sequences in DMF.     

An efficient regioselective reaction of indole with 2H-chromenes for the synthesis of new 4H-chromenes in environmentally benign media

An efficient regioselective, catalyst free, and green protocol has been developed for the synthesis of a novel class of 4H-chromene scaffolds at room temperature in ionic liquid. The method is general and applicable for a series of 2H-chromenes as well as indole derivatives.     

Voacalgines A–E,new indole alkaloids from Voacanga grandifolia

Five new indole alkaloids, voacalgines A–E (1–5) consisting of a C-mavacurine type of skeleton with 2,3-dihydroxybenzoate moiety, a macroline-type of skeleton, or a macroline-type of skeleton with C₆ unit, were isolated from the bark of Voacanga grandifolia. Their relative structures were determined by means of NMR data. Voacalgine A showed moderate cell growth inhibitory activities against HL-60 and HCT116 cells.     

l-Proline catalyzed one-step synthesis of 4,5-diaryl-2H-1,2,3-triazoles from heteroaryl cyanostilbenes via [3+2]cycloaddition of azide

Use of a novel reagent has been established for the synthesis of a series of 4,5-diaryl-2H-1,2,3-triazoles (6a–i and 9a–e) from cyanostilbene analogs of benzo[b]thiophene, benzo[b]furan, and indole, catalyzed by l-proline via Lewis base-catalyzed one-step [3+2]cycloaddition of azide. This method provides an efficient, simple, and environmentally benign procedure that affords good yields and relatively short reaction times.     

One-pot synthesis of disulfide-linked N-sulfonylazetidin-2-imines via a copper-catalyzed multicomponent cascade reaction

A copper-catalyzed, three-component reaction between a sulfonyl azide, an alkyne, and a 2-aminothiophenol derived Schiff base is reported. This novel one-pot procedure involves a click reaction, a formal [2+2] cycloaddition, and S–S coupling, therefore, providing a unique method for the synthesis of novel disulfide-linked N-sulfonylazetidin-2-imines under mild conditions.     

Oxidative C(Sp)–H activation and C–N cleavage of N-methyl amines under transition-metal-free condition for synthesis of methylene-bridged bis-1,3-diketones

A transition-metal-free oxidative methylenation reaction was developed. Methylene-bridged bis-1,3-dicarbonyl compounds were synthesized by oxidative C(Sp³)–H activation and C–N cleavage of N-methyl amines. This novel reaction avoids the use of transition metal catalyst. Furthermore, the reaction are very mild and operational convenient.