- Polycyclic heteroaromatics via hydrazine-catalyzed ring-closing carbonyl-olefin metathesis
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The use of hydrazine-catalyzed ring-closing carbonyl-olefin metathesis (RCCOM) to synthesize polycyclic heteroaromatic (PHA) compounds is described. In particular, substrates bearing Lewis basic functionalities such as pyridine rings and amines, which strongly inhibit acid catalyzed RCCOM reactions, are shown to be compatible with this reaction. Using 5 mol% catalyst loadings, a variety of PHA structures can be synthesized from biaryl alkenyl aldehydes, which themselves are readily prepared by cross-coupling. This journal is
- Cho, Eun Kee,Lambert, Tristan H.,Quach, Phong K.,Sim, Jae Hun,Zhang, Yunfei
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p. 2418 - 2422
(2022/03/08)
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- Annulation of β-naphthols and 4-hydroxycoumarins with vinylsulfonium salts: Synthesis of dihydrofuran derivatives
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A new synthetic approach to dihydrofuran derivatives via the annulation reaction of β-naphthols and 4-hydroxycoumarins with vinylsulfonium salts has been developed. A variety of dihydrofuran derivatives were prepared in moderate to good yields under mild conditions. The products could be readily transformed to the corresponding furans via the dehydrogenation with DDQ.
- Chen, Zi-Cong,Tong, Lang,Du, Zhi-Bo,Mao, Zhi-Feng,Zhang, Xue-Jing,Zou, Yong,Yan, Ming
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supporting information
p. 2634 - 2638
(2018/04/26)
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- Nickel-Catalyzed Boron Insertion into the C2-O Bond of Benzofurans
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Treatment of benzofurans with bis(pinacolato)diboron and Cs2CO3 under nickel-NHC catalysis resulted in the insertion of a boron atom into the C2-O bond of benzofurans to afford the corresponding oxaborins. The scope of benzofuran substrates is wide, and the reactions proceeded without loss of functional groups such as fluoro, methoxy, and ester that are potentially reactive under nickel catalysis. The boron-inserted products proved to be useful building blocks and subsequently underwent a series of transformations, one of which led to the synthesis of fluorescent π-expanded oxaborins.
- Saito, Hayate,Otsuka, Shinya,Nogi, Keisuke,Yorimitsu, Hideki
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supporting information
p. 15315 - 15318
(2016/12/09)
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- Bis(cyclopropenium)phosphines: Synthesis, Reactivity, and Applications
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A straightforward route for the preparation of a set of bis(cyclopropenium)-substituted phosphines is reported. Due to their dicationic nature, these ligands depict an excellent π-acceptor character. The effect of the ligand substituent pattern on the catalytic activity of the metal complexes thereof derived is also studied. Whereas sterically demanding biaryl groups directly attached to the phosphorus atom seem to facilitate elementary steps such as the product release from the catalyst, long chain dialkylamino groups on the cyclopropenium units maximize the catalysts solubility and, thus, allow the use of typical apolar solvents such as toluene. Importantly, all new ligands prepared can be easily handled in air. Finally, the impact of the newly prepared dicationic phosphines in hydroarylation reactions is demonstrated. In particular, their use in the synthesis of several naphtho[1,2-b]furanes and naturally occurring naphthalene derivatives such as Calanquinone C is reported.
- Mehler, Gerlinde,Linowski, Pawel,Carreras, Javier,Zanardi, Alessandro,Dube, Jonathan W.,Alcarazo, Manuel
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p. 15320 - 15327
(2016/10/13)
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- Expanding the Strained Alkyne Toolbox: Generation and Utility of Oxygen-Containing Strained Alkynes
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We report synthetic methodology that permits access to two oxacyclic strained intermediates, the 4,5-benzofuranyne and the 3,4-oxacyclohexyne. In situ trapping of these intermediates affords an array of heterocyclic scaffolds by the formation of one or more new C-C or C-heteroatom bonds. Experimentally determined regioselectivities were consistent with predictions made using the distortion/interaction model and were also found to be greater compared to selectivities seen in the case of trapping experiments of the corresponding N-containing intermediates. These studies demonstrate the synthetic versatility of oxacyclic arynes and alkynes for the synthesis of functionalized heterocycles, while further expanding the scope of the distortion/interaction model. Moreover, these efforts underscore the value of harnessing strained heterocyclic intermediates as a unique approach to building polycyclic heteroatom-containing frameworks.
- Shah, Tejas K.,Medina, Jose M.,Garg, Neil K.
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p. 4948 - 4954
(2016/05/10)
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- A Pincer Ruthenium Complex for Regioselective C-H Silylation of Heteroarenes
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A pincer Ru(II) catalyst for the highly efficient undirected silylation of O- and S-heteroarenes with (TMSO)2MeSiH and Et3SiH is described, producing heteroarylsilanes with exclusive C2-regioselectivity, good functional-group tolerance, and high turnover numbers (up to 1960). The synthetic utility of the silylated products is demonstrated by Pd-catalyzed Hiyama-Denmark cross-coupling under mild conditions. One-pot, two-step silylation and coupling procedures have been also developed.
- Fang, Huaquan,Guo, Le,Zhang, Yuxuan,Yao, Wubing,Huang, Zheng
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p. 5624 - 5627
(2016/11/17)
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- Copper(ii)-catalyzed C-O coupling of aryl bromides with aliphatic diols: Synthesis of ethers, phenols, and benzo-fused cyclic ethers
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A highly efficient copper-catalyzed C-O cross-coupling reaction between aryl bromides and aliphatic diols has been developed employing a cheaper, more efficient, and easily removable copper(ii) catalyst. A broad range of aryl bromides were coupled with aliphatic diols of different lengths using 5 mol% CuCl2 and 3 equivalents of K2CO3 in the absence of any other ligands or solvents to afford the corresponding hydroxyalkyl aryl ethers in good to excellent yields. In this newly developed protocol, aliphatic diols have multilateral functions as coupling reactants, ligands, and solvents. The resulting hydroxyalkyl aryl ethers were further readily converted into the corresponding phenols, presenting a valuable alternative way to phenols from aryl bromides. Furthermore, it was demonstrated that they are useful intermediates for more advanced molecules such as benzofurans and benzo-fused cyclic ethers. This journal is
- Liu, Yajun,Park, Se Kyung,Xiao, Yan,Chae, Junghyun
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p. 4747 - 4753
(2014/06/24)
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- Preparation of phenanthrenes by photocyclization of stilbenes containing a tosyl group on the central double bond. A versatile approach to the synthesis of phenanthrenes and phenanthrenoids
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We have developed a useful modification of the classical preparation of phenanthrenes by UV irradiation of stilbenes in the presence of an oxidant. This modification involves the irradiation, in the presence of base, of stilbenes possessing a sulfonyl group linked to the central double bond. We have proved that this protocol can be successfully applied for the synthesis of diverse phenanthrenes and phenanthrenoids.
- Neo, Ana G.,Lopez, Carmen,Romero, Victor,Antelo, Berta,Delamano, Jose,Perez, Antonio,Fernandez, Dolores,Almeida, Jesus F.,Castedo, Luis,Tojo, Gabriel
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supporting information; experimental part
p. 6764 - 6770
(2010/12/19)
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- An isomerization-ring-closing metathesis strategy for the synthesis of substituted benzofurans
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Twelve substituted benzofurans were synthesized from their corresponding substituted 1-allyl-2-allyloxybenzenes using ruthenium-mediated C- and O-allyl isomerization followed by ring-closing metathesis.
- Van Otterlo, Willem A.L.,Morgans, Garreth L.,Madeley, Lee G.,Kuzvidza, Samuel,Moleele, Simon S.,Thornton, Natalie,De Koning, Charles B.
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p. 7746 - 7755
(2007/10/03)
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- Base-Induced Photocyclization of 1,2-Diaryl-1-tosylethenes. A Mechanistically Novel Approach to Phenanthrenes and Phenanthrenoids
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(Equation presented) The irradiation with UV light of a number of 1,2-diaryl-1-tosylstilbenes, in the presence of base, leads to the corresponding phenanthrenes and heterocyclic analogues. These results are consistent with a mechanism involving the base-induced elimination of p-toluenesulfinic acid from an intermediate 9-tosyl-4a,4b-dihydrophenanthrene, formed by photochemical cyclization of the starting 1,2-diaryl-1-tosylstilbenes.
- Almeida, Jesus F.,Castedo, Luis,Fernandez, Dolores,Neo, Ana G.,Romero, Victor,Tojo, Gabriel
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p. 4939 - 4941
(2007/10/03)
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- Expeditious synthesis of dihydronaphthofurans utilising 1,2-dioxines and stabilised phosphorus ylides
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A new practical synthesis of functionalised 1,2-dihydronaphtho[2,1- b]furans from substituted 2,4a-dihydronaphtho[2,1-c][1,2]dioxines and stabilised phosphorus ylides is described. Functionalised γ-hydroxy enones and their isomeric hemiacetals are key intermediates.
- Haselgrove, Thomas D.,Jevric, Martyn,Taylor, Dennis K.,Tiekink, Edward R. T.
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p. 14739 - 14762
(2007/10/03)
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- Synthesis of peri-cyclobutarenes by thermolysis of [methoxy(trimethylsilyl)methyl]arenes
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[Methoxy(trimethylsilyl)methyl]arenes are readily prepared by reactions of chlorotrimethylsilane with (α-methoxy)arenylmethyllithium reagents as obtained from (methoxymethyl)arenes and t-BuLi. The [methoxy(trimethylsilyl)methyl]arenes eliminate methoxytrimethylsilane at 525-675 °C/0.05-0.10 mm to yield peri-cyclobutarenes as derived from arenylcarbenes. Of importance is the fact that the initial arenylcarbenes generated insert into adjacent peri C-H bonds and/or isomerize to other arenylcarbenes that insert into their peri C-H bonds to give peri- cyclobutarenes. Thus, flash-vacuum pyrolysis of 1- [methoxy(trimethylsilyl)methyl]naphthalene (13) at 575-675 °C/0.05-0.10 mm yields 1H-cyclobuta[de]naphthalene (6, up to 39%) in practical quantities. 2- [Methoxy(trimethylsilyl)methyl]naphthalene (23) also affords 6 as a major thermolysis product. At 510 °C/0.05-0.10 mm 4-methoxy-1- [methoxy(trimethylsilyl)methyl]naphthalene (29) decomposes to 4-methoxy-1H- cyclobuta[de]naphthalene (31, 46%). Under similar conditions, 2-methoxy-1- [methoxy(trimethylsilyl)methyl]naphthalene (33) converts to 1,2- dihydronaphtho[2,1-b]furan (35, 64%) and naphtho[2,1-b]furan (36, 31%), presumably by insertion of 2-methoxy-1-naphthylcarbene (34) into a C-H bond of its o-methoxy group and then dehydrogenation of the resultant dihydrofuran. Further, 1-[methoxy(trimethylsilyl)methyl]-6-methylnaphthalene (39) pyrolyzes (510 °C/0.10-0.20 mm) to 6-methyl-1-naphthylcarbene (40), which isomerizes in part to 7-methyl-1-naphthylcarbene (49); carbenes 40 and 49 then undergo peri C-H insertion to give 3-methyl-1H- cyclobuta[de]naphthalene (41) and 2-methyl-1H-cyclobuta[de]naphthalene (42) in an 8:1 ratio and a combined yield of 44%. The pyrolytic method is particularly valuable for preparing higher peri single carbon atom bridged arenes such as 4H-cyclobuta[jk]phenanthrene (53, 65%) and 3H- cyclobuta[cd]pyrene (59, 86%).
- Engler, Thomas A.,Shechter, Harold
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p. 4247 - 4254
(2007/10/03)
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- Synthesis of fused furans by gas-phase pyrolysis of 2-allyloxyaryl-propenoic esters
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Flash vacuum pyrolysis of 2-allyloxypropenoic esters (e.g. 7) gives benzo[b]furans (e.g. 32) in synthetically useful yields by sequential generation of a phenoxyl radical, cyclisation and ejection of the carboxylic ester function as a free radical leaving group. The method is compatible with a range of substituents on either the benzene ring or the propenoate chain, and is particularly effective for 2-substituted benzo[b]furans. The natural products 5-methoxybenzo[b]furan 1 and angelicin 2 have been synthesised in three and four steps respectively from commercially available starting materials by this route. Related cyclisations to give naphtho[2,1-b]furan 40 were complicated by competitive formation of naphtho[2,1-b]pyran-3-ones (e.g. 41 and 42), but the yield of the required product could be optimised by the choice of the radical precursor. Annelation of a furan ring onto a thlophene is also possible by this method, but lower yields are obtained in such pyrolyses.
- Black, Michael,Cadogan,McNab, Hamish,MacPherson, Andrew D.,Roddam, V. Peter,Smith, Carol,Swenson, Helen R.
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p. 2483 - 2493
(2007/10/03)
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- Carboxylic Esters as Radical Leaving Groups: A New and Efficient Gas-phase Synthesis of Benzofurans
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Flash vacuum pyrolysis (FVP) of o-allyloxycinnamate esters gives benzofurans in high yield, via cyclisation of a phenoxyl radical and subsequent cleavage of the carboxylic ester function; coumarins are obtained by FVP of the corresponding phenols.
- Black, Michael,Cadogan, J. I. G.,Cartwright, Gary A.,McNab, Hamish,MacPherson, Andrew D.
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p. 959 - 960
(2007/10/02)
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- FORMATION OF 1-CHLOROBENZOCYCLOBUTENE, ANTHRACENE OR BENZOFURAN BY FLASH VACUUM PYROLYSIS
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Pyrolysis of o-substituted benzylidene chlorides is shown to be a useful route to 1-chlorobenzocyclobutene, anthracene or benzofurans; evidence is given for a carbene intermediate in the pyrolysis of o-methoxybenzylidene chloride.
- Hussain, Amjad,Parrick, John
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p. 609 - 612
(2007/10/02)
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- PERI-METHANOARENES BY THERMOLYSIS OF TRIMETHYLSILANES
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Practical syntheses of varied peri-methanoarenes have been developed.
- Engler, T. A.,Shechter, H.
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p. 2715 - 2718
(2007/10/02)
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