Search

Comprehensive Summary: An efficient and highly stereoselective synthetic method to access polycyclic chromanes has been achieved through organocatalyzed one‐pot step‐wise reactions involving 2‐hydroxycinnamaldehydes, 2‐aminochalcones, and malononitrile as substrates. The reactions underwent a quintuple process by aza‐Michael/Michael/Knoevenagel/oxa‐Michael/aldol‐type reaction in sequence to give products bearing 3 new generated rings and 5 chiral centers in moderate to quantitative yields with excellent stereoselectivities. A novel retro‐reaction mechanism was discovered in the synthetic transformations of products. [ABSTRACT FROM AUTHOR]

A novel CoII -catalyzed polyene cyclization was developed that is uniquely effective when performed in hexafluoroisopropanol as the solvent. The process is presumably initiated by metal-catalyzed hydrogen-atom transfer (MHAT) to 1,1-disubstituted or monosubstituted alkenes, and the reaction is remarkable for its tolerance of internal alkenes bearing either electron-rich methyl or electron-deficient nitrile substituents. Electron-rich aromatic terminators are required in both cases. Terpenoid scaffolds with different substitution patterns are obtained with excellent diastereoselectivities, and the bioactive C20-oxidized abietane diterpenoid carnosaldehyde was made to showcase the utility of the nitrile-bearing products. Also provided are the results of several mechanistic experiments that suggest the process features an MHAT-induced radical bicyclization with late-stage oxidation to regenerate the aromatic terminator.

Gold(I)‐catalyzed cyclization of o‐alkenyl‐o'‐alkynylbiaryls in the presence of external or internal nucleophiles provides a straightforward access to phenanthrene‐based polycycles, which are of considerable interest in materials science. Thus, their reactions with alcohols yield functionalized dihydrophenanthrenes, in a process that can also be carried out intramolecularly, to provide phenanthrene‐derived heteropolycyclic compounds. Moreover, benzo[b]triphenylenes can be synthesized from o‐methoxyvinyl‐o'‐alkynylbiaryls, in a reaction in which an (hetero)aryl substituent at the triple bond acts as an internal nucleophile. [ABSTRACT FROM AUTHOR]

A two‐step synthesis of less accessible spiro[cyclobutene‐1,9′‐fluorene] compounds from biaryl‐alkynes and 2‐(2‐fluoropyridin‐1‐ium‐1‐yl)‐1,1‐bis((trifluoromethyl)sulfonyl)ethan‐1‐ide, which serves as a potent precursor for outstandingly electrophilic Tf2C=CH2, has been developed. This synthetic methodology includes selective formation of gem‐bis(triflyl)cyclobutenes from biaryl‐alkynes and Tf2C=CH2 followed by desulfinative spirocyclisation mediated by 1,1,1,3,3,3‐hexafluoroisopropyl alcohol (HFIP). Besides, on the basis of the chameleonic reactivity of sulfone functionality, several derivatisations of triflylated spiro[cyclobutene‐1,9′‐fluorene] products have been successfully achieved. [ABSTRACT FROM AUTHOR]

The synthesis of several centrotriindanes bearing ortho‐phenyl groups in the sterically constricted bay regions is described. The classical three‐step sequence including twofold cyclodehydration of the corresponding 2,2‐dibenzyl‐1,3‐indanediols afforded an angular difuso‐triidane and several all‐cis‐tribenzo[5.5.5.6]fenestranols equipped with two or four ortho‐phenyl groups. In contrast to the construction of these conformationally flexible centrotriindanes, attempts to synthesize ortho,ortho‐diphenyl‐substituted tribenzotriquinacenes failed due to the increased rigidity of the TBTQ skeleton. The high steric load imposed by the para‐terphenyl moieties affects the spirocyclization between 1,3‐indanedione and 1,5‐di‐(para‐2′‐terphenylyl)pentadienone, kinetic control of which is critical to access the all‐cis‐tribenzo[5.5.5.6]fenestrane framework. In contrast, the corresponding tetraphenyl‐cis,cis,cis,trans‐tribenzo[5.5.5.6]fenestranol is easily accessible. [ABSTRACT FROM AUTHOR]

The carboarylation reaction of biphenyl‐alkynes was successfully triggered by electrophilic attack of 1,1‐bis(triflyl)ethylene on the alkyne moiety to give polycyclic aromatic hydrocarbons (PAHs) decorated by superacidic carbon acid functionality. Neutralisation of thus obtained acids with NaHCO3 yielded the corresponding sodium salts, which showed improved solubility in both aqueous and organic solvents. [ABSTRACT FROM AUTHOR]

Here we demonstrate an approach to graft bis(heteroaryl)‐containing motifs into ring structures. The process occurs by redirecting a previously reported oxadiazole‐forming reaction towards a pyrazole‐forming process affording pyrazolyl‐azole containing molecules. Through the use of (N‐isocyanimino)phosphorane (Pinc), heteroatom‐rich fused tricyclic heterocycles can be synthesized in a single step from readily accessible starting materials. The cyclization of peptides results in macrocycles that feature bis(heteroaryl) motifs with uncommon connectivity as compared to their natural counterparts. [ABSTRACT FROM AUTHOR]

The Scholl‐type cyclodehydrogenation, generating up to four cycloheptatriene rings around a fenestrindane core, leads to novel, saddle‐shaped polyaromatic hydrocarbon derivatives. In this article, we present the results of in‐depth experimental and computational work on the oxidative cyclization of various 1,4,9,12‐tetraarylfenestrindanes. In particular, the kinetic control of the four‐step cyclization of the electronically activated tetrakis(3,4‐dimethoxyphenyl) derivative is elucidated. The reasons for the exclusive emergence of one single among the three possible doubly cyclized intermediates and for the nonappearance of the singly and triply cyclized intermediates are clarified. In addition, the origin of the concomitant bridgehead hydroxylation is studied. The reactivity of a set of fifteen symmetrically and unsymmetrically substituted 1,4,9,12‐tetraarylfenestrindanes towards Scholl‐type cyclodehydrogenation is presented, pinpointing the structural factors that underlie this reaction and demonstrating the potential and limitations of this synthetic approach. A particularly surprising finding of this study is that the electronically nonactivated 1,4,9,12‐tetraphenylfenestrindane can also undergo the fourfold Scholl‐type cyclization process and can be transformed into the parent saddle hydrocarbon. [ABSTRACT FROM AUTHOR]

A new method to prepare phenanthro[9,10‐c]thiophenes has been developed. In the presence of triflic acid, 3,4‐diaryl thiophenes undergo 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ)‐promoted cyclo‐oxidation. NMR and computational studies indicate that protonation of the thiophene plays a key role in this reaction. The reaction can be used to prepare phenanthro[9,10‐c]thiophene, as well as derivatives with alkyl, bromo, and methoxy substituents. However, the yields and selectivity of the reaction depend on both the nature and location of the substituents. Bis(3‐methoxyphenyl)thiophene reacts under these conditions to give the desired product in 57 % yield, while bis(4‐methoxyphenyl)thiophene gives no product. Bis(3‐bromophenyl)thiophene did not react, but cyclo‐oxidation of bis(4‐bromophenyl)thiophene provides the desired product in 34 % yield. [ABSTRACT FROM AUTHOR]

Enantiopure N‐benzyl 6‐oxopipecolic acid, obtained from (S)‐2‐aminoadipic acid, was evaluated under π‐cationic cyclization conditions. If the combination of SOCl2/AlCl3 seems to be superior in terms of the reaction yields, use of PPA, (CF3CO)2O/BF3·Et2O, and Eaton's reagent is also very interesting since in addition to the expected keto‐lactam, reduced‐ and oxidized keto‐lactam, enamides and enamidones containing CF3CO– residue are isolated. Mechanisms leading to these products as well as the ones resulting from their acidic treatment were proposed and discussed with the help, in some cases, of univocal transformations and X‐ray analysis. Enantiopure N‐benzyl 6‐oxopipecolic acid, generated from (S)‐2‐aminoadipic acid, was evaluated under different π‐cationic cyclization conditions. The combination of SOCl2/AlCl3 seems to be superior in terms of the reaction yields. Other activators resulted in a change of the reaction profile and, interestingly, in the diversification of the aza‐heterocyclic systems. [ABSTRACT FROM AUTHOR]

Promising test results on the biological activity of our previously described naphtho[1,2‐d]oxazoles and heterobenz[1,2‐d]oxazoles, obtained by the photochemical cyclization of 5‐phenylethenyl‐ and 5‐heteroarylethenyloxazoles, prompted us to continue with the photochemical synthesis of substituted naphtho[1,2‐d]oxazoles, and to extend the photochemical cyclization to the synthesis of naphtho/heterobenz[2,1‐d]oxazoles from 4‐(aryl/heteroarylethenyl)oxazoles. The required p‐ and o‐phenyl‐substituted 5‐arylethenyloxazoles were prepared from the corresponding α,β‐unsaturated aldehydes and the TosMIC reagent (tosylmethyl isocyanide) by the Van Leusen reaction. The substituted 4‐(aryl/heteroarylethenyl)oxazoles were prepared by the Wittig reaction starting from various phosphonium salts and 2‐H/methyl‐4‐oxazolecarbaldehydes. [ABSTRACT FROM AUTHOR]

A methodology for the synthesis of indolo[1,2-b]isoquinoline derivatives by Lewis acid-catalyzed intramolecular Friedel–Crafts alkylation reaction has been developed. The reaction proceeds well with both secondary and primary 2-indolylmethanols. The method efficiently affords pharmaceutically important polycyclic fused indole derivatives in moderate to high yields with good functional group tolerance. In addition, the reaction proceeded in large scale indicating that this method could be scaled up for the synthesis of indolo[1,2-b] isoquinoline derivatives. [ABSTRACT FROM AUTHOR]

The synthesis of highly functionalized spirocarbocyclic oxindoles was accomplished for the first time, using a Hauser annulation strategy. A reaction between methylene-indolinones and arylsulfonylphthalides catalyzed by cesium carbonate gave access to a new class of biologically important spiro[indoline-3,2'-naphthalene] derivatives in very good yields. [ABSTRACT FROM AUTHOR]

Reported is the enantioselective synthesis of tetracyclic indolines using silver(I)/chiral phosphoric acid catalysis. A variety of alkyne-tethered indoles are suitable for this process. Mechanistic studies suggest that the in situ generated silver(I) chiral phosphate activates both the alkyne and the indole nucleophile in the initial cyclization step through an intermolecular hydrogen bond and the phosphate anion promotes proton transfer. In addition, further modifications of the cyclization products enabled stereochemistry-function studies of a series of bioactive indolines. [ABSTRACT FROM AUTHOR]

Cyclic ethers are widely abundant in natural products. Cyclic ether templates are also utilized in drug design and medicinal chemistry. Although the synthetic processes for this class of compounds have been studied extensively with respect to five-and six-membered rings, medium-sized cyclic ethers are synthetically more challenging due to a variety of factors. Herein, we report our results on the Lewis acid catalyzed synthesis of medium-sized cyclic ethers in a diastereoselective manner. [ABSTRACT FROM AUTHOR]

A new strategy has been developed for the synthesis of spirofluorenyl benzosultams through the annulation of aryl iodides with cyclic N-sulfonyl ketimines. This method uses a readily available PdII catalyst for the activation of aryl C--H bonds to facilitate the annulation process. Pd is cheaper than other transition metal catalysts commonly used for the C--H activation, such as Ir and Rh. This approach leads to the synthesis of biologically relevant spiro-benzosultams in a single-step process. [ABSTRACT FROM AUTHOR]

Cyclic polymers are an important class of macromolecules, but the structural diversity of the backbone is limited. Herein we report the use of the Piers-Rubinsztajn reaction for the one-step synthesis of cyclic polysiloxanes with novel structural features. Specifically, the B(C6F5)3-catalyzed coupling of various organic tris(dimethylsiloxy)silane and trialkoxysilane compounds generated a series of cyclic polysiloxanes with cyclotetrasiloxane subunits. The thiolated cyclic polymers were also shown to be effective in directing the circular assembly gold nanoparticles. The presence of constrained rings in the backbone is unprecedented and may offer opportunities for novel applications of these cyclic polymers. [ABSTRACT FROM AUTHOR]

An extensive study of the chemoselective Pd-catalyzed inter- and intramolecular direct C-H arylation of N-benzylated 5-carboxyimidazoles with halides with and without CuI assistance in 1,4-dioxane as a low-polarity solvent was explored. The method was suitable for the synthesis of fused imidazole-based tricyclic systems incorporating medium-sized rings, including, for the first time, eight-membered rings, which are valuable in modern drug design. [ABSTRACT FROM AUTHOR]

The addition of a nicotinate-xanthate derivative to N-allylindoles and N-allylpyrroles resulted in polycyclic heterocycle-fused pyridonaphthyridines through a tandem radical intermolecular/intramolecular oxidative addition reaction sequence that created three new C-C bonds and two new rings in a single event. Such polyheterocycles showcase the matrine alkaloid framework and are similar to indole-monoterpenoid natural products. [ABSTRACT FROM AUTHOR]

Numerous procedures have been described for the functionalization of pyrazolo[3,4- b]pyridine, mainly involving nucleophilic substitutions at the C-4 position or esterifications/amidations at the C-5 position. In this paper, we describe a robust, easy to implement protocol for the Suzuki cross-coupling reaction of chloroarene 2, followed by in-situ lactonization to provide chromenopyrazolopyridines. The extension of the scope of the reaction to fused naphthyridinones is also reported. This strategy gave access to 10 original pyrazolopyridine-containing tetracyclic compounds. [ABSTRACT FROM AUTHOR]

β-Amyrin synthase incubation experiments have been conducted to determine the influence of steric effects at the 6-, 10- and 15-positions of 2,3-oxidosqualene on the polycyclisation pathway. Nor- and ethyl-substituted oxidosqualene analogues were synthesised. Cyclisation of the ethyl-substituted analogues did not occur, but the nor analogues underwent a polycyclisation cascade to yield fully cyclised products with 6/6/6/6/6-fused pentacyclic scaffolds generated via a final oleanyl cation. Previously, we reported that 19- and 23-ethyl-substituted analogues underwent polycyclisation reactions. Therefore, the catalytic domain involved in earlier cyclisation steps is notably compact. In contrast, the catalytic domain in the later cyclisation steps is more loosely packed (less compact) to accommodate the bulky ethyl group. The reaction cavities for recognising branched methyl groups are discussed by comparing β-amyrin synthase with other triterpene cyclases such as lanosterol and hopene synthases. [ABSTRACT FROM AUTHOR]

The cycloaromatization of aromatic aldehydes and ketones was readily achieved by using a Brønsted acid catalyst in 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP). In the presence of a catalytic amount of trifluoromethanesulfonic acid, biaryl-2-ylacetaldehydes and 2-benzylbenzaldehydes underwent sequential intramolecular cationic cyclization and dehydration to afford phenacenes and acenes, respectively. Furthermore, biaryl-2-ylacetaldehydes bearing a cyclopentene moiety at the α-position underwent unprecedented cycloaromatization including ring expansion to afford triphenylenes. HFIP effectively promoted the cyclizations by suppressing side reactions presumably as a result of stabilization of the cationic intermediates. [ABSTRACT FROM AUTHOR]

The first synthesis of racemic 2‐(aminomethyl)cyclopropane‐1,1‐dicarboxylic acid was developed involving sequential iodocarbocyclization, azidation, saponification and reduction of dimethyl 2‐allylmalonate. The developed synthetic pathway avoids reactions such as ring opening of the cyclopropane ring toward acyclic δ‐amino carboxylic acid derivatives or lactamisation toward bicyclic methyl 3‐aza‐2‐oxobicyclo[3.1.0]hexane‐1‐carboxylates which occur in alternative synthetic strategies. [ABSTRACT FROM AUTHOR]

A new synthesis of substituted acridines is achieved by palladium-catalyzed addition of terminal acetylenes between the aryl rings of bis(2-bromophenyl)amine. By including a diamine base and elevating the temperature, the reaction pathway favors the formation of acridine over a double Sonogashira reaction to form bis(tolan)amine. This method is demonstrated with several aryl-alkynes and alkyl-alkynes.

Enantioselective syntheses of (-)-alloyohimbane and (-)-yohimbane were accomplished in a convergent manner. The key step involves a modified mild protocol for the enantioselective enzymatic desymmetrization of a meso-diacetate. This provides convenient access to an optically active monoacetate in multi-gram quantities and in high enantiomeric purity. This monoacetate was converted to (-)-alloyohimbane. Reductive amination of the derived aldehyde caused isomerization to the trans-product and, ultimately, the formation of (-)-yohimbane. [ABSTRACT FROM AUTHOR]

Implementation of non-planar aromatic motifs in the molecular design of π-conjugated materials represents a paradigm shift that is interesting from a fundamental research viewpoint but remains largely underdeveloped. To further facilitate this cause, we report on the synthesis and properties of two large polycyclic aromatic compounds (38 carbon atoms). In one compound the planar π-system pyrene is linked to bowl-shaped hydrocarbon corannulene through a C=C bond, which is referred to as 'corannulene-vinylpyrene'. Photochemical treatment of this compound results in annulation of both aromatic nuclei and formation of the other large fused structure with ten six-membered aromatic rings, referred to as 'corannulene-benzopyrene'. Photophysical and electrochemical studies reveal that the properties of these two structurally related hybrid materials arise from an extended π-conjugation between the planar and non-planar motifs and varies depending upon their molecular structure. [ABSTRACT FROM AUTHOR]

A total synthesis of riccardin C has been accomplished using a Corey-Seebach reaction to effect macrocyclisation. The versatility of the strategy has also been demonstrated with a mimetic synthesis of an unnatural bis(bibenzyl) analogue. [ABSTRACT FROM AUTHOR]

A new synthetic sequence including two sequential multicomponent reactions leading to a wide range of thiazolo- and oxazoloannulated benzodiazepinediones is described. This strategy features simple one-pot operations under mild conditions in combination with a high degree of diversity, and can be realized based on commercially available or easily accessible starting materials. [ABSTRACT FROM AUTHOR]

A cycloaddition reaction promoted by the Lewis acid BF3 ·OEt2 between 2-arylidene-1,3-indanediones and β-enamino esters, generated by the addition of arylamines to dimethyl acetylenedicarboxylate, gave densely substituted 1,4-diphenyl-4,5-dihydro-1 H-indeno[1,2- b]pyridines in satisfactory yields. When 2-isatylidene-1,3-indanediones were used under the same conditions, the one-pot reaction gave the corresponding spiro[indeno[1,2- b]pyridine-4,3′-indolines] in high yields. On the other hand, unusual 1,2-diphenyl-2,5-dihydro-1 H-indeno[1,2- b]pyridines were obtained in moderate to good yields through a four-component reaction. [ABSTRACT FROM AUTHOR]

The radical cascade cyclization of various 1,6-enynes with aryl radicals by electron catalysis under metal-free reaction conditions was explored. Readily available anilines were used as radical precursors, and the reactions proceeded in the absence of any transition metal. These cascades comprise three C-C bond formations, which provide polycyclic structures with extended π-systems. The photophysical properties of some of these novel compounds were investigated, and a plausible reaction mechanism is proposed. [ABSTRACT FROM AUTHOR]

A facile and efficient potassium hydroxide (KOH)-catalyzed tandem reaction involving sequential Michael addition of electron-deficient alkenes with malonic esters, ring opening of activated aziridines and lactamization has been described. A highly functionalized indane-fused tricyclic scaffold containing three rings, three adjacent stereocenters and a quaternary center was constructed by the formation of two new C-C bonds and one new C-N bond in a diastereoselective manner. [ABSTRACT FROM AUTHOR]

1-Aryl-1,2,3,4-tetrahydroisoquinolines (THIQ) are key intermediates and products in the pharmaceutical industry. A new method involving intramolecular nucleophilic addition of α-amino carbanions to in-situ-generated arynes in N-Boc-protected (Boc = tert-butoxycarbonyl) amine substrates is presented for the synthesis of these compounds. Surprisingly, a similar reaction in Lewis-acid-complexed tertiary amines failed. These results have been analysed using quantum chemical calculations on the intermediates involved in the reactions. [ABSTRACT FROM AUTHOR]

An efficient, one-pot methodology of direct synthesis of perylene-fused cyclic ketones from perylene and 2-alkenoic acids under acidic catalytic conditions has been developed. The reaction of perylene with 2,3-disubstituted 2-alkenoic acid leads, via Friedel-Crafts acylation followed by Nazarov cyclization, to the formation of disubstituted 5,6-dihydro-4 H-cyclopenta[ b]perylen-4-ones in high yield (up to 97 %) and high diastereoselectivity, whereas the reaction with acrylic acid leads, via alkylation followed by intramolecular Friedel-Crafts acylation, to 2,3-dihydro-1 H-benzo[ cd]perylen-1-one. [ABSTRACT FROM AUTHOR]

The Diels-Alder reactivity of maleic anhydride towards the bay regions of planar polycyclic aromatic hydrocarbons was explored computationally in the DFT framework. The process becomes more and more exothermic and the associated activation barriers become lower and lower when the size of the system increases. This enhanced reactivity follows an exponential behavior that reaches its maximum for systems having 18-20 benzenoid rings in their structures. This peculiar behavior was analyzed in detail by using the activation strain model of reactivity in combination with energy decomposition analysis. The influence of the change in the aromaticity of the polycyclic compound during the process on the respective activation barriers was also studied. [ABSTRACT FROM AUTHOR]

A one-pot synthesis of new oxindole-fused polycyclic scaffolds is reported. The process involves a three-component [3+2] cycloaddition followed by cyclization through an intramolecular Michael addition. The reaction gives easy access to oxindole-fused spirotetrahydrofurochromans in moderate to good yields with high regio- and diastereoselectivity. These compounds could be useful for for drug discovery. Further modification was achieved by reduction of the nitro group, and intramolecular amide formation to give the corresponding lactams. The resulting heterocyclic products show good inhibitory activity against the enzyme PTP1B in vitro. [ABSTRACT FROM AUTHOR]

A one-pot synthesis of new oxindole-fused polycyclic scaffolds is reported. The process involves a three-component [3+2] cycloaddition followed by cyclization through an intramolecular Michael addition. The reaction gives easy access to oxindole-fused spirotetrahydrofurochromans in moderate to good yields with high regio- and diastereoselectivity. These compounds could be useful for for drug discovery. Further modification was achieved by reduction of the nitro group, and intramolecular amide formation to give the corresponding lactams. The resulting heterocyclic products show good inhibitory activity against the enzyme PTP1B in vitro. [ABSTRACT FROM AUTHOR]

A three-component bicyclization strategy for the efficient synthesis of densely functionalized pyrazolo[3,4- d]thiazolo[3,2- a]pyrimidines from readily accessible aryl aldehydes, α-thiocyanate ketones, and pyrazol-5-amines was established. The reaction pathway involves a nucleophilic addition/5- exo-trig/6- endo-trig bicyclization sequence that results in continuous multiple bond-forming events, including the formation of C-N and C-C bonds, to give high levels of molecular complexity. [ABSTRACT FROM AUTHOR]

A convenient synthetic route to novel 7-substituted benzo[ f]thieno[3,2- h]quinazoline and 8-substituted benzo[ g, h]dithieno[2,3- e:3′,2′- j]perimidine systems, bearing the fused pyrimidine ring, has been advanced. A commercially available 5-bromopyrimidine was used as the starting material to obtain various polycyclic systems through the sequence of nucleophilic aromatic substitution of hydrogen (the SNH reaction), Suzuki cross-coupling and oxidative photocyclization. Evidence for the structure of benzo[ g, h]dithieno[2,3- e:3′,2′- j]perimidines has been obtained by X-ray crystallographic analysis. Molecular orbital calculations (DFT), as well as redox and optical measurements for all new compounds have been performed. The data show that the reported polycyclic systems have potential for use in organic electronic applications. [ABSTRACT FROM AUTHOR]

Regioselective access to 6-aryl-5-iodobenzo[ e]pyrido[1,2- a]indoles was realized by using a facile 6- endo- dig iodine-mediated cyclization under mild reaction conditions. Further functionalization of the resulting products by using Pd-catalyzed coupling reactions was demonstrated, leading to the tetracyclic core substituted with two distinct functional groups in a regioselective fashion. [ABSTRACT FROM AUTHOR]

The synthesis of novel heterocyclic [1,2,4]triazolo[3,4- b][1,3,4]thiadiazine hybrids by a bimolecular reaction of 2-(4-amino-5- mercapto-4H-[1,2,4]triazol-3-yl)phenol with an aromatic or heterocyclic α-bromoacetyl derivatives is described. This synthetic procedure starts from an unprotected phenol. [ABSTRACT FROM AUTHOR]

The copper-catalyzed double intramolecular Ullmann coupling of syn-1,2-bis(2-bromoaryl)ethane-1,2-diols with catalytic amounts of CuII oxinate as the copper source, K3PO4 as a base, and KI as a reductant in aqueous acetonitrile selectively delivers 4b,9b-dihydrobenzofuro[3,2-b]benzofurans in diastereomerically and enantiomerically pure form and yields of up to 90%. The substrates can be obtained in both diastereomerically and enantiomerically pure form by catalytic dihydroxylation of the corresponding (E)-stilbenes. [ABSTRACT FROM AUTHOR]

Detailed insights gained from our research into the gas-phase chemistry of ionized and protonated diphenylalkanes and their congeners, obtained by extended synthesis of isotopically labeled model compounds and mass spectrometry, are presented and merged with those acquired during our development of a new family of polycyclic hydrocarbons, the centropolyindanes. Aside from a Personal Account that describes "two scientific lives in one", it is demonstrated, on the one hand, how our understanding of organic chemistry can help to shed light on the details of mass spectrometric fragmentation and to unravel, in a more fundamental way, the unimolecular reactivity of gaseous ions. On the other hand, it is shown how unexpected reactivity of related ions in solution, being subject to the very same fundamentals of organic chemistry, can lead to the construction of novel and, in part, unique three-dimensional polycyclic structures that may contribute to future research in material science.Two such apparently independent fields of organic chemistry may be seen as joint contributions of the art of science. [ABSTRACT FROM AUTHOR]

[5]Phenacene with trimethylsilyl groups at the axis positions was synthesized by the ruthenium-catalyzed direct C−H arylation of a 1-formyl-7-phenanthrene-derived aldimine, followed by sequential Wittig olefination and bismuth-catalyzed cyclization of the resulting vinyl ethers. By using the same synthetic building blocks and sequential Wittig olefination and photocyclization, the number of fused benzene rings was readily increased to seven to afford 3,12-disilyl[7]phenacene. The introduction of silyl groups endowed the [ n]phenacene frameworks with good solubility, as well as enabling further functionalization. The electronic structure of these new [ n]phenacenes was determined by photophysical measurements and by density functional theory calculations, which clearly implied effective conjugation throughout the entire π framework. [ABSTRACT FROM AUTHOR]

Oxidosqualene cyclases catalyze the transformation of oxidosqualene ( 1) into numerous cyclic triterpenes. Enzymatic reactions of 24-noroxidosqualene ( 8) and 30-noroxidosqualene ( 9) with Euphorbia tirucalli β-amyrin synthase were conducted to examine the role of the branched methyl groups of compound 1 in the β-amyrin biosynthesis. Substrate 8 almost exclusively afforded 30-nor-β-amyrin (>95.5 %), which was produced through a normal cyclization pathway, along with minor products (<4.5 %). However, a lack of the Me-30 group (analogue 9) resulted in significantly high production of premature cyclization products, including 6/6/6/5-fused tetracyclic and 6/6/6/6/5-fused pentacyclic skeletons (64.6 %). In addition, the fully cyclized product (35.4 %) having the 6/6/6/6/6-fused pentacycle was produced; however, the normally cyclized product, 29-nor-β-amyrin was present in only 18.6 % of these products. The conversion yield of substrate 8 possessing a Z-Me group at the terminus was approximately twofold greater than that of compound 9 with an E-Me group. Thus, the Me-30 group is essential for the correct folding of a chair-chair-chair-boat-boat conformation of compound 1 for the production of the β-amyrin scaffold, whereas the Me-24 group exerts little influence on the normal polycyclization cascade. Here, we show that the Me-30 group plays critical roles in constructing the ordered architecture of a chair-chair-chair-boat-boat structure, in facilitating the ring-expansion reactions, and in performing the final deprotonation reaction at the correct position. [ABSTRACT FROM AUTHOR]

Synthetic efforts toward the rapid assembly of the AB ring system of the tetrapetalones is described. Key to this work was the use of [3+2] cycloaddition/oxidative extrusion methodology to furnish functionalized aryl enones. The Nazarov cyclization of these substrates was examined, and optimized to generate the AB ring carbon skeleton. Then, Pd-catalyzed cross-coupling were conducted, and conditions were identified that enabled installatiion of the requisite C14–N bond. [ABSTRACT FROM AUTHOR]

New hexacyclo and octacyclo compounds have been synthesized by a short route whose key step consists of a single or double domino nucleophilic substitution of neopentyl-type iodides with potassium cyclopentadienide, followed by intramolecular Diels-Alder cycloaddition. [ABSTRACT FROM AUTHOR]

A generic approach to the regiospecific synthesis of halogenated polycyclic aromatics is made possible by the one- or two-directional benzannulation reactions of readily available ( ortho-allylaryl)trichloroacetates (the 'BHQ' reaction). Palladium-catalysed cross-coupling reactions of the so-formed haloaromatics enable the synthesis of functionalised polycyclic aromatic hydrocarbons (PAHs) with surgical precision. Overall, this new methodology enables the facile mining of chemical space in search of new electronic functional materials. [ABSTRACT FROM AUTHOR]