Palladium-catalyzed potassium enoxyborate alkylation of enantiopure Hajos-Parrish indenone to construct rearranged steroid ring systems

Here we report the stereo- and regiospecific C-6 alkylation of a trans-inden-5-one (from optically pure Hajos-Parrish ketone) with allylic electrophiles. Use of this alkylation procedure has led to an improved synthesis of the benz[f]indene ring system and the first enantiospecific total syntheses of the cyclopenta[b]anthracene and cyclopenta[b]phenanthrene ring systems (two synthetic routes).     

Strained polycycles by H5C5x free-radical cascades

[reaction: see text] An H(5)C(5x)-type free-radical chain reaction selectively generates up to three new bonds and three new stereocenters in one pot. This previously unexploited strategy provides a straightforward route to the tricyclic cyclopenta[c]indene skeleton, present in a wide range of pharmacologically active natural products, and can significantly simplify the synthesis of other strained polycyclic structures by sidestepping protection, deprotection, and functional group interconversion steps.     

Ni-catalyzed intramolecular cycloaddition of methylenecyclopropanes to alkynes

Ni-catalyzed intramolecular cycloaddition of methylenecyclopropanes (MCPs) to arkylalkynes via proximal bond cleavage is reported. The reaction provides a facile route for the preparation of cyclopenta[a]indene derivatives.     

Biomimetic Total Synthesis of Cyanosporaside Aglycons from a Single Enediyne Precursor through Site‐Selective p‐Benzyne Hydrochlorination

The cyanosporasides A–F are a collection of monochlorinated benzenoid derivatives isolated from the marine actinomycetes Salinispora and Streptomyces sp. All derivatives feature one of two types of cyanocyclopenta[a]indene frameworks, which are regioisomeric in the position of a single chlorine atom. It is proposed that these chloro‐substituted benzenoids are formed biosynthetically through the cycloaromatization of a bicyclic nine‐membered enediyne precursor. Herein, we report the synthesis of such a bicyclic precursor, its spontaneous transannulation into a p‐benzyne, and its differential 1,4 hydrochlorination reactivity under either organochlorine or chloride‐salt conditions. Our bioinspired approach culminated in the first regiodivergent total synthesis of the aglycons A/F and B/C, as well as cyanosporasides D and E. In addition, empirical insights into the site selectivity of a natural‐like p‐benzyne, calculated to be a ground‐state triplet diradical, to hydrogen, chlorine, and chloride sources are revealed.     

A catalytically active,charge-neutral Rh(I) zwitterion featuring a P,N-substituted "naked" indenide ligand

The synthesis and characterization of a new class of cationic and zwitterionic Rh(I) complexes, which feature multidentate ligands comprised of donor-functionalized indene or indenide units, are reported. This unusual new ligation strategy provides access to the first charge-neutral [kappa2-P,N]Rh(I) zwitterion, a complex that functions as a catalyst for the C-H/Si-H dehydrogenative coupling of styrene and triethylsilane.     

The effect of ethynyl substitution and cyclopenta fusion on the ultraviolet absorption spectra of polycyclic aromatic hydrocarbons

We have examined the UV spectra of six newly-synthesized ethynyl-PAH (1-ethynylnaphthalene, 5-ethynylacenaphthylene, 1-ethynylanthracene, 9-ethynylphenanthrene, 3-ethynylfluoranthene, and 1-ethynylpyrene) and five corresponding CP-PAH (acenaphthylene, aceanthrylene, acephenanthrylene, cyclopenta[cd]fluoranthene, and cyclopenta[cd]pyrene) and have found the following systematic behavior: ethynyl-substitution results in average bathochromic shifts of 5 nm for the lower-wavelength beta- and beta'-bands and of 18 nm for the higher-wavelength p-band, as well as an amplification of the p-band with respect to the beta-band; the addition of a peripheral cyclopenta ring results in average bathochromic shifts of 7 nm in the beta-band, 16 nm in the beta'-band, and 44 nm in the p-band, compared to the wavelengths in the corresponding unsubstituted PAH. The addition of a cyclopenta ring also decreases the resolution of vibrational fine structure in the cases where the fine structure is particularly intense in the spectrum of the unsubstituted PAH. The effects of ethynyl substitution on the UV spectra of PAH are sufficiently consistent that new ethynyl-PAH should be identifiable based on their UV spectra alone.     

Palladium-catalyzed cycloisomerizations of diarylacetylenes: synthesis, structures, and physical properties of highly substituted naphthalenes and 8,8 a-dihydrocyclopenta[a]indenes

Depending on the electronic properties of their substituents, the major products generated by palladium‐catalyzed cycloisomerizations of diarylalkynes are either highly substituted 8,8a‐dihydrocyclopenta[a]indenes 3 or naphthalenes 4 . The structures of these compounds were verified by X‐ray crystallographic analysis. Many functional groups tolerated the reaction conditions evaluated in this study. The isotope‐labeled experiments indicated that added water has a critical role in forming both classes of compounds. The photophysical and electrochemical properties of cycloadducts 3 and their analogues were systematically studied and compared with computational predictions based on density functional theory. Dihydrocyclopenta[a]indenes 3 in either solid or liquid form display strong luminescence, whereas cyclopenta[a]indene 11 j is practically nonfluorescent. The functional groups directly attached to the backbone of compound 3 significantly influenced physical properties. The steric effect arising from the aryl substituents caused different luminescence phenomena, including aggregation‐induced and ‐enhanced emission.     

Stereoselective [3+2] Carbocyclization of Indole‐Derived Imines and Electron‐Rich Alkenes: A Divergent Synthesis of Cyclopenta[b]indole or Tetrahydroquinoline Derivatives

An unprecedented stereoselective [3+2] carbocyclization reaction of indole‐2‐carboxaldehydes, anilines, and electron‐rich alkenes to obtain cyclopenta[b]indoles is disclosed. This pathway is different from the well‐established Povarov reaction: the formal [4+2] cycloaddition involving the same components, which affords tetrahydroquinolines. Moreover, by simply changing the Brønsted acid catalyst, this multicomponent coupling process could be divergently directed towards the conventional Povarov pathway to produce tetrahydroquinolines or to the new pathway (anti‐Povarov) to generate cyclopenta[b]indoles. Supported by computational studies, a stepwise Mannich/Friedel–Crafts cascade is proposed for the new anti‐Povarov reaction, whereas a concerted [4+2] cycloaddition mechanism is proposed for the Povarov reaction.     

A novel acid-catalyzed transformation of octadienynedial derivatives to cyclopenta[b]-thiapyrans and cyclopenta[b]pyran.

Substituted 2,6-octadien-4-ynedial derivatives were synthesized, which give cyclopenta[b]thiapyran or cyclopenta[b]pyran derivatives by intramolecular cyclization.     

Cyclopenta[c]selenophene based cooligomers and their polymers: comparative study with thiophene analogues

Selenophene and thiophene capped cyclopenta[c]selenophenes were synthesized and characterized. Crystal structure determination of some representative compounds revealed that the substitution at 3,4-position in the form of cyclopentane ring of selenophene or thiophene does not make any significant twist in the trimer backbone, making the cooligomer nearly planar. All the cooligomers were electrochemically polymerized and compared with thiophene capped cyclopenta[c]thiophene polymer. DFT calculations predict that the cyclopentane substitution on the third repeating unit (and in general) of one dimensional polymer neither disturb the planarity nor causes any significant twist on the polymeric backbone unlike the 3,4-dialkyl substitution. The electrochemically prepared selenophene based polymers showed low band gap compared to that of thiophene analogues. Cyclopentane substitution on selenophene as well as thiophene makes the resulting polymer oxidatively more stable when compared to more familiar poly-ethylenedioxythiophene (PEDOT) or poly-ethylenedioxyselenophene (PEDOS) systems. Alternate polymers of cyclopenta[c]selenophenes (CPS)/cyclopenta[c]thiophene (CPT) and thiophene/selenophene possess the energy of HOMO and LUMO significantly lower than that of homopolymers of CPS and CPT, however, possess higher band gap than PCPS.     

Traceless solid-phase synthesis of heterosteroid framework

[reaction: see text]A traceless solid-phase synthesis of cyclopenta[c]-4H-chromen-8-ol, benzo[d]cyclopenta[e]-3H-3-azin-8-ol, and other 11-heterosteroids via the fulvene hetero [6 + 3] cycloaddition is described.     

Condensation of fluorine-substituted benzaldehydes with amines and cyclic ketones

Condensation of fluorine-containing benzaldehydes with naphthalen-2-amine or quinolin-6-amine and cyclic ketones (cyclopentanone, cyclohexanone, and 4-methylcyclohexanone) gave new fluorine-containing derivatives of cyclopenta[c]benzo[f]quinoline, benzo[a]phenanthridine, and cyclopenta[a]- and benzo[a]-[4,7]phenanthroline. Intermediate products, 2-[(fluorophenyl)(2-naphthylamino or quinolin-6-ylamino)methylidene] cyclohexanones, dihydrobenzo[f]quinolines, and dihydro-4,7-phenanthrolines, were isolated.     

Intrinsically microporous polyimides containing spirobisindane and phenazine units: Synthesis,characterization and gas permeation properties

A new diamine containing spirobisindane and phenazine units, namely, 3,3,3′,3′‐tetramethyl‐2,2′,3,3′‐tetrahydro‐1,1′‐spirobi[cyclopenta[b]phenazine]‐7,7′‐diamine (TTSBIDA) was synthesized starting from commercially available 5,5′,6,6′‐tetrahydroxy‐3,3,3′,3′‐tetramethyl‐1,1′‐spirobisindane (TTSBI). TTSBI was oxidized to 3,3,3′,3′‐tetramethyl‐2,2′,3,3′‐tetrahydro‐1,1′‐spirobi[indene]‐5,5′,6,6′‐tetraone (TTSBIQ) which was subsequently condensed with 4‐nitro‐1,2‐phenylenediamine to obtain 3,3,3′,3′‐tetramethyl‐7,7′‐dinitro‐2,2′,3,3′‐tetrahydro‐1,1′‐spirobi[cyclopenta[b]phenazine] (TTSBIDN). TTSBIDN was converted into TTSBIDA by reduction of the nitro groups using hydrazine hydrate in the presence of Pd/C as the catalyst. A series of new polyimides of intrinsic microporosity (PIM‐PIs) were synthesized by polycondensation of TTSBIDA with commercially available aromatic dianhydrides. PIM‐PIs exhibited amorphous nature, high thermal stability (T₁₀ > 480 °C) and intrinsic microporosity (BET surface area = 59–289 m²/g). The gas permeation characteristics of films of selected PIM‐PIs were evaluated and they exhibited appreciable gas permeability as well as high selectivity. The CO₂ and O₂ permeability of PIM‐PIs were in the range 185.4–39.2 and 30.6–6.2 Barrer, respectively. Notably, polyimide derived from TTSBIDA and 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (PIM‐PI‐6FDA) exhibited high CO₂ and O₂ permeability of 185.4 and 30.6 Barrer with CO₂/CH₄ and O₂/N₂ selectivity of 43.1 and 5.1, respectively. The data of PIM‐PI‐6FDA for CO₂/CH₄ and O₂/N₂ gas pairs were located near Robeson upper bound. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 766–775     

An AB + D → ABCD approach to the construction of the 8-azasteroid skeleton by [3+3] cyclocondensation of 3,4-dihydroisoquinolines with ethyl 2-oxocyclopentanecarboxylate as a new annelation reaction for a series of cyclic Schiff"s bases

A new approach (AB + D ABCD) to the construction of tetracyclic 8-azagonane (cyclopenta[5,6]pyrido[2,1-a]isoquinoline or benzo[a]cyclopenta[f]quinolizine) structures was developed and exemplified by cyclocondensation of 1-alkyl-3,4-dihydroisoquinolines with ethyl 2-oxocyclopentanecarboxylate.     

Flash vacuum thermolysis of acenaphtho[1,2-a]acenaphthylene. Thermal behaviour of a polycyclic aromatic hydrocarbon containing two abutting pentagons

FVT of acenaphtho[1,2-a]acenaphthylene (1) gave acenaphtho[1,2-e]acenaphthylene (2), cyclopenta[cd]perylene (3) and cyclopenta[rst]benzo[hi]chrysene (4). The formation of 3 and 4 indicates that, besides ring contraction/ring expansion of 1 giving 2, homolytic scission of a five-membered ring carbon---carbon single bond of 1 is an important competitive process.     

Synthesis of the 2,5-di-t-butyl-cyclopenta[a]pentalenide ion: A novel 12π-electron system

The resonance destabilized, paratropic lithium 2,5-di-t-butyl-cyclopenta [a] pentalenide has been prepared as the first derivative of the cyclopenta [a] pentalenide ion.     

Synthesis of New Cyclopenta[<Emphasis Type="Italic">b</Emphasis>]quinoline Derivatives

A series of new 11-(R-phenyl)-8,9-dihydro-7H-benzo[f]cyclopenta[b]quinolin-10(11H)-ones and 7,14-bis(R-phenyl)-2,3,9,10,11,14-hexahydrocyclopenta[2,3]quinolino[8,7-h]cyclopenta[b]quinoline-1,8(4H,7H)-diones were synthesized by three-component condensation of naphthalen-2-amine or naphthalene- 1,5-diamine with substituted benzaldehydes and cyclopentane-1,3-dione in one step through intermediate formation of unstable arylaminoketoenol.     

Pyrylation of 1,2-diphenylbenzo[b]cyclopenta[e]pyran

1,2-Diphenylbenzo[b]cyclopenta[e]pyran was pyrylated with 2,6-diphenylpyrylium perchlorate. The structures of the singly and doubly charged 2,6-diphenyl-4-(1,2-di-phenylbenzo[b]cyclopenta[e]-3-pyrania)pyrylium cations are confirmed by data from the electronic absorption spectra. A radical mechanism for the pyrylation is proposed on the basis of the ESR spectrum.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 459–461, April, 1978.     

First synthesis of enantiopure 1,6-difunctionalized dodecahydrobenz[f]indenes

An enantiospecific route to the previously unreported 1,6-difunctionalized dodecahydrobenz[f]indene ring system is described. Optically pure Hajos-Parrish ketone is used as the building block for preparation of a 6-methyleneinden-5-ol. This allylic alcohol is then utilized in a Claisen rearrangement under Johnson's conditions to introduce a side chain that is further modified and cyclized to produce the benz[f]indene ring system.     

Structural specificity of electrophilic substitution of reaction of 2-phenylbenzo[b]cyclopenta[e]pyran

2-Phenyl- and 1,2-diphenylbenzo[b]cyclopenta[e]pyrans were subjected to formylation, nitration, and phenylsufonylation. It was shown by PMR spectroscopy that 2-phenylbenzo[b]cyclopenta[e]pyran undergoes substitution exclusively in the 1 position. The effect of the spatial orientation and the degree of electron-acceptor character of the introduced substituents on the chemical shift of the 9-H proton was studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 902–905, July, 1977.