An Efficient Synthesis of Optically Active trans‐(3R,4R)‐3‐Acetoxy‐4‐aryl‐1‐(chrysen‐6‐yl)azetidin‐2‐ones Using (+)‐Car‐3‐ene as a Chiral Auxiliary

An efficient enantioselective synthesis of 3‐acetoxy trans‐β‐lactams 7a and 7b via [2+2] cycloaddition reactions of imines 4a and 4b , derived from a polycyclic aromatic amine and bicyclic chiral acid obtained from (+)‐car‐3‐ene, is described. The cycloaddition was found to be highly enantioselective, producing only trans‐(3R,4R)‐N‐azetidin‐2‐one in very good yields. This is the first report of the synthesis of enantiomerically pure trans‐β‐lactams 7a and 7b with a polycyclic aromatic substituent at N(1) of the azetidin ring.     

Synthesis of dimethyl heterocyclic‐o‐dicarboxylates using dimethyl acetylenedicarboxylate

Dimethyl acetylenedicarboxylate (DMAD) is a very important and useful reagent for the preparation of dimethyl heterocyclic‐o‐dicarboxylates, which are key intermediates in the synthesis of fused pyridazine derivatives. The synthesis of thiopyranes by the Diels‐Alder reaction of dithiocarboxylate derivatives, synthesis of various cyclazines by [2 + 8] cycloaddition reactions, and synthesis of dimethyl pyrazolo[3,4‐b]pyridine‐5,6‐dicarboxylates and polycyclic heterocycles containing the 1,6‐naphthyridine ring system by the reaction of o‐aminonitrile compounds with DMAD are described here.     

Intramolecular Aza‐Diels–Alder Reactions of ortho‐Quinone Methide Imines: Rapid,Catalytic, and Enantioselective Assembly of Benzannulated Quinolizidines

Aza‐Diels–Alder reactions (ADARs) are powerful processes that furnish N‐heterocycles in a straightforward fashion. Intramolecular variants offer the additional possibility of generating bi‐ and polycyclic systems with high stereoselectivity. We report herein a novel Brønsted acid catalyzed process in which ortho‐quinone methide imines tethered to the dienophile via the N substituent react in an intramolecular ADAR to form complex quinolizidines and oxazinoquinolines in a one‐step process. The reactions proceed under very mild conditions, with very good yields and good to very good diastereo‐ and enantioselectivities. Furthermore, the process was extended to a domino reaction that efficiently combines substrate synthesis, ortho‐quinone methide imine formation, and ADAR.     

Synthesis of New Schiff Bases and Polycyclic Fused Thiopyranothiazoles Containing 4,6‐Dichloro‐1,3,5‐Triazine Moiety

New aromatic aldimines, isatine substituted ketimines based on (4,6‐dichloro‐1,3,5‐triazin‐2‐yl)‐hydrazine scaffold and polycyclic fused thiopyranothiazoles formed using hetero‐Diels‐Alder reactions starting from 4‐thioxo‐2‐thiazolidinones and 5‐norbornene‐2,3‐dicarboxylic acid triazino‐derivatives synthetic approach is described. The application of condensation and cyclocondensation reactions of N‐nucleophiles and carbonyl agents for synthesis a number of biologically active triazine derivatives is reported. Screening of anticancer activity in vitro yielded the most active compounds 3a , 8b , and 8f for different cell lines.     

Intermolecular Photocyclizations of N‐(ω‐Hydroxyalkyl)tetrachlorophthalimide with Alkenes Leading to Medium‐ and Large‐Ring Heterocycles—Reaction Modes and Regio‐ and Stereoselectivity of the 1,n‐Biradicals

A new photocyclization strategy by using intermolecular tandem reactions between N‐(ω‐hydroxyalkyl)‐4,5,6,7‐tetrachlorophthalimides ( 1 , 2 , and 3 ) and a series of acyclic and cyclic alkenes is reported. Electron transfer of the triplet‐excited phthalimide with the alkene and regioselective trapping of the alkene cation radical by the hydroxyl group at the phthalimide side chain gives a triplet 1,n‐biradical, which after intersystem crossing (ISC) leads to regio‐ and diastereoselective synthesis of polycyclic heterocycles with an N,O‐containing medium to large ring. Regio‐ and diastereoselectivity in the cyclizations are clarified by unambiguous steric structure assignments of the products by X‐ray diffraction or extensive 2D NMR measurements. The diastereoselectivity is decided by the stereochemical course of the ISC process of the triplet 1,n‐biradicals. These intermolecular photoreactions also furnish a new strategy to generate triplet 1,n‐biradicals. Therefore, in photoreactions of 1 and 2 with phenylcyclohexene, the unprecedented stereoselective formation of products by intramolecular hydrogen‐atom transfer in the 1,n‐biradical intermediate was found ( 9 and 23 ). These facts provide direct verification to the reaction pathways of the 1,n‐biradicals and give a new insight into the factors deciding reaction‐pathway partitioning and stereoselectivity.     

One‐Step Annulative π‐Extension of Alkynes with Dibenzosiloles or Dibenzogermoles by Palladium/o‐chloranil Catalysis

Reliable and short synthetic routes to polycyclic aromatic hydrocarbons and nanographenes are important in materials science. Herein, we report an efficient one‐step annulative π‐extension reaction of alkynes that provides access to diarylphenanthrenes and related nanographene precursors. In the presence of a cationic palladium/o ‐chloranil catalyst system and dibenzosiloles or dibenzogermoles as π‐extending agents, a variety of diarylacetylenes are transformed successfully into 9,10‐diarylphenanthrenes in a single step with good functional‐group tolerance. Furthermore, double π‐extension reactions of 1,4‐bis(phenylethynyl)benzene and diphenyl‐1,3‐butadiyne are demonstrated, affording oligoarylene products, which show potential for application in the synthesis of larger polycyclic aromatic hydrocarbons and nanographenes.     

Bio‐inspired Domino oxa‐Michael/Diels–Alder/oxa‐Michael Dimerization of para‐Quinols

A bio‐inspired, pyrrolidine‐mediated, dimerization of para‐quinols has been developed. It represents one of the most complex, yet general, dimerization reactions ever disclosed, selectively forming four new bonds, four new rings, and eight new contiguous stereogenic centres. The para‐quinol starting materials are easily handled, bench‐stable compounds, accessed in just one step from aromatic feedstocks. The reaction can be scaled up to give grams of polycyclic material, primed for further elaboration.     

Heptagon‐Embedded Pentacene: Synthesis,Structures, and Thin‐Film Transistors of Dibenzo[d,d′]benzo[1,2‐a:4,5‐a′]dicycloheptenes

This study presents a new class of conjugated polycyclic molecules that contain seven‐membered rings, detailing their synthesis, crystal structures and semiconductor properties. These molecules have a nearly flat C₆‐C₇‐C₆‐C₇‐C₆ polycyclic framework with a p‐quinodimethane core. With field‐effect mobilities of up to 0.76 cm² V^?1 s^?1 as measured from solution‐processed thin‐film transistors, these molecules are alternatives to the well‐studied pentacene analogues for applications in organic electronic devices.     

Heptagon‐Embedded Pentacene: Synthesis,Structures, and Thin‐Film Transistors of Dibenzo[d,d′]benzo[1,2‐a:4,5‐a′]dicycloheptenes

This study presents a new class of conjugated polycyclic molecules that contain seven‐membered rings, detailing their synthesis, crystal structures and semiconductor properties. These molecules have a nearly flat C₆‐C₇‐C₆‐C₇‐C₆ polycyclic framework with a p‐quinodimethane core. With field‐effect mobilities of up to 0.76 cm² V⁻¹ s⁻¹ as measured from solution‐processed thin‐film transistors, these molecules are alternatives to the well‐studied pentacene analogues for applications in organic electronic devices.     

A Facile Synthesis of Bridged Polycyclic Naphthooxazocine Skeletons: Eight‐Membered‐Ring Constructions via Tandem Dinucleophilic Addition of Naphthalenols to Quinolinium Salts

The efficient synthesis of bridged polycyclic naphthooxazocines 3 via addition of naphthalenols 1 as a bis‐nucleophile to N‐alkylquinolinium salts 2 is described (Scheme 1 and Table 2). This new approach provides a powerful entry into polycyclic structures containing bicyclic N,O‐acetals related to bioactive compounds.     

Synthesis of new 5‐acetyl(arylmethyliden)‐4‐thiazolidones

A new approach to the synthesis of new heterocyclic compounds with triazine and 4‐thiazolidone fragments in one molecule is developed. The synthesis methods comprise [2+3]‐cyclocondensation reactions essential in the preparative synthesis of 4‐thiazolidone derivatives. The reactions of S,N‐nucleophiles with C₂‐cyclization agents for the synthesis of a number of biologically active 2‐triazin‐4‐thiazolidones were investigated. The interaction of thiosemicarbazone of sym‐triazine with derivatives of α‐halogencarboxylic acids and maleic anhydride resulted in correspondent (2‐[2‐(4,6‐dichloro‐1,3,5‐triazin‐2‐yl)hydrazino]‐5‐(3,4,5‐ R‐p‐phenyl‐methyliden)‐1,3‐thiazol‐4‐ones obtained in the one‐step synthesis. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:392–396, 2010; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20631     

Diversity‐oriented Construction of Chromanone‐fused Polycyclic Pyrrolidinyl‐dispirooxindoles

Achieved herein is a novel diversity‐oriented one‐pot multicomponent synthesis of polycyclic pyrrolidinyl‐dispirooxindoles 3 . The key pyrrolidine forming reaction is the 1,3‐dipolar cycloaddition event of isatylidenyl‐chromanones 2 with azomethine ylides (thermally generated in situ from isatins and proline or thioproline). Products bearing four consecutive stereocenters consist of two oxindole moieties and a pyrrolidinyl core, including vicinal spiroquaternary stereocenters fused in one ring structure, were smoothly obtained in high yields (up to 89% yield) with good diastereoselectivity (up to >20:1). Valuable feature of this method was the design of new hybrid architectures for biological screenings through creating molecular diversity and complexity by means of the generation of several bonds and rings in a single operation. In particular, their biological activity against human leukemia cells K562 and normal L929 cells have been evaluated. These results suggested changes of this chromanone group could obviously impact the activity, and a chromanone group located in the polycyclic pyrrolidinyl‐dispirooxindoles is beneficial for the activity. What is more, the results also indicated that chromanone‐fused polycyclic pyrrolidinyl‐dispirooxindoles 3 have selective cytotoxicity against cancer cells K562 compared with normal cells L929.     

Ligand‐free,copper‐catalyzed,one‐pot,three‐component synthesis of novel 1,2,3‐triazole‐linked indoles in magnetized water

Magnetized water (MW) is used as a green and new solvent‐promoting medium for the one‐pot, three‐component synthesis of novel 1,2,3‐triazole‐linked indoles catalyzed by copper iodide. A broad range of 2‐aryl‐1‐(prop‐2‐ynyl)‐1H‐indole‐3‐carbaldehydes were reacted with alkyl halides and sodium azide via copper‐catalyzed azide–alkyne cycloaddition reactions in MW in the absence of any ligand. This method offers the advantages of short reaction times, green procedure, low cost, simple work‐up, quantitative reaction yields, and no need for any organic solvent.     

Cu‐Catalyzed Aerobic Oxidative Cyclizations of 3‐N‐Hydroxyamino‐1,2‐propadienes with Alcohols,Thiols, and Amines To Form α‐O‐, S‐, and N‐Substituted 4‐Methylquinoline Derivatives

A one‐pot, two‐step synthesis of α‐O‐, S‐, and N‐substituted 4‐methylquinoline derivatives through Cu‐catalyzed aerobic oxidations of N‐hydroxyaminoallenes with alcohols, thiols, and amines is described. This reaction sequence involves an initial oxidation of N‐hydroxyaminoallenes with NuH (Nu=OH, OR, NHR, and SR) to form 3‐substituted 2‐en‐1‐ones, followed by Brønsted acid catalyzed intramolecular cyclizations of the resulting products. Our mechanistic analysis suggests that the reactions proceed through a radical‐type mechanism rather than a typical nitrone‐intermediate route. The utility of this new Cu‐catalyzed reaction is shown by its applicability to the synthesis of several 2‐amino‐4‐methylquinoline derivatives, which are known to be key precursors to several bioactive molecules.     

π‐Extended Star‐Shaped Polycyclic Aromatic Hydrocarbons based on Fused Truxenes: Synthesis,Self‐Assembly,and Facilely Tunable Emission Properties

A new set of star‐shaped polycyclic aromatic hydrocarbons (PAHs) based on naphthalene‐fused truxenes, TrNaCn (n=1–4), were synthesized and characterized. The synthesis involved a microwave‐assisted six‐fold Suzuki coupling reaction, followed by oxidative cyclodehydrogenation. Multiple dehydrocyclization products could be effectively isolated in a single reaction, thus suggesting that the oxidative cyclodehydrogenation reaction involved a stepwise ring‐closing process. The thermal, optical, and electrochemical properties and the self‐assembly behavior of the resulting oxidized samples were investigated to understand the impact of the ring‐fusing process on the properties of the star‐shaped PAHs. Distinct bathochromic shift of the absorption maxima (λ_max) revealed that the molecular conjugation extended with the stepwise ring‐closing reactions. The optical band‐gap energy of these PAHs varied significantly on increasing the number of fused rings, thereby resulting in readily tunable emissive properties of the resultant star‐shaped PAHs. Interestingly, the generation of rigid “arms” by using perylene analogues caused TrNaC2 and TrNaC3 to show significantly enhanced photoluminescence quantum yields (PLQYs) in solution (η=0.65 and 0.66, respectively) in comparison with those of TrNa and TrNaC1 (η=0.08 and 0.16, respectively). Owing to strong intermolecular interactions, the TrNa precursor was able to self‐assemble into rod‐like microcrystals, which could be facilely identified by the naked eye, whilst TrNaC1 self‐assembled into nanosheets once the naphthalene rings had fused. This study offers a unique platform to gain further insight into—and a better understanding of—the photophysical and self‐assembly properties of π‐extended star‐shaped PAHs.     

One‐pot Synthesis of Benzamidonaphtho[2,1‐b]furans and Benzamidobenzo[b]furans as Novel Polycyclic Heteroaromatic Compounds

An operationally simple, green and efficient procedure for one‐pot synthesis of novel polycyclic heteroaromatic compounds such as benzamidonaphtho[2,1‐b]furans and benzamidobenzo[b]furans has been developed from the reaction of arylglyoxals, benzamide, and phenols. The reactions were mediated with low amounts of yttrium nitrate hexahydrate as a suitable Lewis acid catalyst without using solvent.     

The Synthesis and Chemistry of 1,3‐Bridged Polycyclic Cyclopropenes: 8‐Oxatricyclo[3.2.1.02,4]octa‐2,6‐dienes

Three 1,3‐bridged polycyclic cyclopropenes, exo‐8‐oxatricyclo[3.2.1.0^2,4]octa‐2,6‐diene ( 10 ), endo‐8‐oxatricyclo[3.2.1.0^2,4]octa‐2,6‐diene ( 11 ), and exo‐6,7‐benzo‐1,5‐diphenyl‐8‐oxatricyclo[3.2.1.0^2,4]octa‐2,6‐diene ( 12 ), have been synthesized by elimination of 2‐chloro‐3‐trimethylsilyl‐8‐oxatricyclo[3.2.1.0^2,4]‐oct‐6‐enes, 17 , 18 and 30 , which were generated from 1‐chloro‐3‐trimethylsilylcyclopropene with furan and diphenylisobenzofuran. We have demonstrated a facile route to synthesize the highly strained 1,3‐fused polycyclic cyclopropenes, 10 , 11 , and 12 . The stereochemistry of the Diels‐Alder reactions of cyclopropene 16 with furan and DPIBF are different. Cyclopropene 16 was treated with furan to form exo‐exo and endo‐exo adducts (5:2) and treated with DPIBF to generate an exo‐exo adduct. Compounds 10 , 11 and 12 undergo isomerization reactions to form benzaldehyde and phenyl 4‐phenyl‐[1]naphthyl ketone to release strain energies via diradical mechanisms.     

Synthesis of 3,4‐Dihalogenated Furan‐2‐(5 H)‐ones by Electrophilic Cyclization of 4‐Hydroxy‐2‐alkynoates

Functionalized 3,4‐dihalogenated furan‐2(5 H)‐ones can be readily prepared in moderate to good yields by treating 4‐hydroxy‐4‐arylbut‐2‐ynoate derivatives with ICl, IBr, and I₂. Both halogen atoms of the electrophile are incorporated in the product. The resulting halides can further afford polycyclic aromatic compounds using known palladium‐catalyzed coupling reactions.     

Facile One‐pot,Three‐component Synthesis of Novel Bis‐heterocycles Incorporating 5H‐chromeno[2,3‐b]pyridine‐3‐carbonitrile Derivatives

Novel bis‐chromeno[2,3‐b ]pyridine derivatives were synthesized with good yields by a clean and efficient methodologies involving one‐pot three‐component synthesis of bis‐aldehydes, malononitrile dimer, and dimedone in the presence of piperidine as a catalyst in EtOH. Depending on the length and position of the spacer in the bis‐aldehyde derivatives 1 , the reactions proceeded to give either the bis(2,4‐diamino‐tetrahydro‐5H‐chromeno[2,3‐b ]pyridine‐3‐carbonitriles) 4 or bis(4‐amino‐2,6‐dioxo‐hexahydro‐2H‐chromeno[2,3‐b ]pyridine‐3‐carbonitriles) 5 . All of the new compounds have been characterized by spectral data.     

A Photoredox‐Induced Stereoselective Dearomative Radical (4+2)‐Cyclization/1,4‐Addition Cascade for the Synthesis of Highly Functionalized Hexahydro‐1H‐carbazoles

A stereoselective synthesis of functionalized hexahydrocarbazoles was developed based on an unprecedented photoredox‐induced dearomative radical (4+2)‐cyclization/1,4‐addition cascade between 3‐(2‐iodoethyl)indoles and acceptor‐substituted alkenes. The title reaction simultaneously generates three C−C bonds and one C−H bond, along with three contiguous stereogenic centers. The hexahydro‐1H ‐carbazole products are highly valuable intermediates for the synthesis of novel antibiotics, as well as unnatural ring homologues of polycyclic indoline alkaloids.