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The development of a Lewis acid-catalyzed, intramolecular ring-opening benzannulation of 5-(indolyl)2,3-dihydrofuran acetals is described. The resulting 1-hydroxycarbazole-2-carboxylates are formed in up to 90% yield in 1 h. The dihydrofuran acetals are readily accessed from the reactions of enol ethers and α-diazo-β-indolyl-β-ketoesters. To highlight the method’s synthetic utility, a formal total synthesis of murrayafoline A, a bioactive carbazole-containing natural product, was undertaken.

A mild and efficient synthesis of a broad scope of substituted naphtho[1,2-a]pyrene derivatives was accomplished in good yields using an InCl3/AgNTf2-mediated two-fold alkyne benzannulation reaction. HPLC enantiomeric separation was achieved and the interconversion barriers have been determined. The ECD spectra of two derivatives were recorded and interpreted through TD-DFT calculations. Raman spectra were also recorded and predicted through DFT calculations.

TiCl4 (or SnCl4)-promoted hetero-type benzannulation reactions using various (2,2-dichlorocyclopropyl)(thiophen-2-yl)methanols proceeded smoothly to produce uniquely substituted 4-chlorobenzothiophenes (five examples). The present approach involves the first distinctive thiophene formation from thiophene cores, in contrast to traditional methods of thiophene formation from benzene cores. The stereocongested (less reactive) Cl position in the obtained 4-chlorobenzothiophenes functioned successfully as the partners of three cross-coupling reactions: (i) a Suzuki–Miyaura cross-couplings using Pd(OAc)2/SPhos/K3PO4 catalysis (seven examples, 63–91%), (ii) a hydroxylation using KOH/Pd(dba)2/tBu-XPhos catalysis (85%), and (iii) a borylation using a B2(pin)2/Pd(dba)2/XPhos/NaOAc catalysis-provided 4-(pin)B-benzothiophene (58%).

Herein we report a significant, valuable extension of a recently implemented pyrrole benzannulation methodology that, employing versatile nitrodienes from our lab as useful C4 building blocks, led to indole derivatives characterized by unusual patterns of substitution. The 6-nitro-7-arylindoles resulting from suitably derivatized, non-symmetric dienes are of foreseeable synthetic interest in search for new polyheterocyclic systems. As an example, pyrrolocarbazoles with a rarely reported ring fusion were synthesized with the classical Cadogan protocol. Furthermore, the proven easy reducibility of the nitro group to amine will surely open the way to further interesting elaborations.

Divergent and enantiospecific total syntheses of the indolosesquiterpenoids xiamycins A, C, F, H and oridamycin A have been accomplished. The syntheses, which commence from (R)-carvone, employ a key photoinduced benzannulation sequence to forge the carbazole moiety characteristic of these natural products. Late-stage diversification from a common intermediate enabled the first syntheses of xiamycins C and F, and an unexpected one-pot oxidative decarboxylation, which may prove general, led to xiamycin H. All synthetic intermediates and the natural products were tested for anti-fungal activity. Xiamycin H emerged as an inhibitor of three agriculturally relevant fungal pathogens.

We report herein an original protocol to the indole nucleus, which could contribute to significantly expand the synthetic access to a heterocyclic moiety of undeniable paramount importance. The protocol consists in the construction of the benzene ring onto a pyrrole (benzannulation) starting from 2,3-dinitro-1,3-butadienes. This appealing, metal-free process characterized by high atom economy and mild reaction conditions allows to synthesize indoles possessing nitro group(s) on the benzene ring: a result which cannot be likewise easily obtained by exploiting most common pathways such as functionalization of a preformed indole or heteroannulation of a suitable benzene derivative. From a mechanistic point of view, a stepwise, ionic process is suggested by the identification of a pivot dihydroindole intermediate whose interception facilitates some selectivity in the preparation of different nitroindoles.

The extension of π-conjugation of polycyclic aromatic hydrocarbons (PAHs) via alkyne benzannulation reactions has become an increasingly utilized tool over the past few years. This short review will highlight recent work of alkyne benzannulations in the context of large nanographene as well as graphene nanoribbon synthesis along with a brief discussion of the interesting physical properties these molecules display.

A series of atropisomeric molecules containing the indole ring and two stereogenic axes were prepared. The four atropisomers were resolved by enantioselective HPLC. The rotational barriers of the indole–naphthyl axes were evaluated by means of kinetic analysis either by NMR or enantioselective HPLC. The absolute configuration of the ­atropisomers was determined by a combination of X-ray spectroscopy and TD-DFT simulation of electronic circular dichroism spectra.

The synthesis of four N-functionalized bis[1]benzothieno[3,2-b:2&prime, 3&prime, d]pyrroles (BBTPs) is reported in order to provide a more detailed characterization of these fused-ring units, as well as increase the scope of known BBTP units available for application to conjugated materials. The optical, electronic, and structural properties of the resulting BBTP units have been compared to the parent N-alkyl- and N-aryl-dithieno[3,2-b:2&prime, d]pyrroles (DTPs), as well as their corresponding 2,6-diphenyl derivatives, in order to fully quantify the relative electronic effects resulting from benzannulation of the parent DTP building block. Such comparative analysis reveals that benzannulation results in a red-shifted absorbance, but to a lesser extent than simple phenyl-capping of the DTP. More surprising is that benzannulation results in stabilization of the BBTP HOMO, compared to the destabilization normally observed with extending the conjugation length of the backbone.

A new route has been reported for the synthesis of densely oxygenated polycyclic aromatic compounds via cycloaddition approach. This strategy involves the Dotz benzannulation and Diels-Alder reaction as key steps. Naphthalene synthons required here were generated by Dotz benzannulation between aryl chromium carbene complexes and symmetrical internal alkyne. (C) 2016 Elsevier Ltd. All rights reserved.

A concise stereoselective synthesis of the tetracyclic naphthoquinone natural product (-)-isagarin has been completed in seven steps from known alkyne 5 (obtained from D -mannitol) by using Dotz benzannulation and intramolecular stereospecific dioxabicyclic ketal formation as key steps.

Methodology has been developed for laying down a thin gold-on-silver film on the inner surface of glass capillaries for the purpose of catalysing benzannulation reactions. The cycloaddition precursors are flowed through these capillaries while the metal film is being heated to high temperatures using microwave irradiation. The transformation can be optimized rapidly, tolerates a wide number of functional groups, is highly regioselective, and proceeds in good to excellent conversion.

A new approach to the synthesis of the 6H-benzo[d]naphtha[1,2-b]pyran-6-one ring system present in the gilvocarcin family of antibiotics is described. The key feature of this approach is the application of a new benzannulation strategy (the 'BHQ Reaction') whereby readily available ortho-allylaryl trichloroacetates are transformed into naphthalene derivatives via a cascade of reactions involving an initial ATRC reaction followed by the extrusion of CO2. © 2009 Elsevier Ltd. All rights reserved.

The development of a formal synthesis of aflatoxin B2 is described, which utilizes a Dötz benzannulation reaction as a key step. © 2007 Elsevier Ltd. All rights reserved.

International audience; The formation of 1-acyl-2,2-diphenylcyclopropanes is performed under mild electrochemical conditions. These cyclopropane derivatives, through acid-catalyzed ring-opening, lead to γ,γ-diphenyl-β,γ-unsaturated carbonyl compounds which evolve into either substituted naphthalenes, or β-benzhydryl-α,β-cycloalkenones depending on the acyclic or cyclic nature of the intermediate allyl ketone.1-Acyl-2,2-diphenylcyclopropanes prepared under mild electrochemical conditions, are converted, in acidic medium, first into γ,γ-diphenyl-β,γ-unsaturated ketones and subsequently into substituted naphthalenes or β-benzhydryl-α,β-cycloalkenones.