- Rhodium(III)-catalyzed transannulation of cyclopropenes with n-phenoxyacetamides through C-H activation
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An efficient rhodium(III)-catalyzed synthesis of 2H-chromene from N-phenoxyacetamides and cyclopropenes has been developed. The reaction represents the first example of using cyclopropenes as a three-carbon unit in rhodium(III)- catalyzed C(sp2)-H activations.
- Zhang, Hang,Wang, Kang,Wang, Bo,Yi, Heng,Hu, Fangdong,Li, Changkun,Zhang, Yan,Wang, Jianbo
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- Acid-promoted cyclization of 2-propynolphenols leading to 4-tosyloxy-2H-chromenes
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A novel and efficient p-TsOH-promoted cascade cyclization of 2-propynolphenols is developed to give 4-tosyloxy-2H-chromenes in moderate to efficient yields. It is noted that p-TsOH acts not only as a promoter in this reaction, and also as the sulfonate source. Importantly, the obtained 4-tosyloxy-2H-chromenes can be used as versatile intermediates for the synthesis of various functionalized compounds through diverse metal-catalyzed cross-coupling reactions. Moreover, this method can be enlarged to gram scale.
- Li, Ren,Jin, Fengyan,Song, Xian-Rong,Yang, Tao,Ding, Haixin,Yang, Ruchun,Xiao, Qiang,Liang, Yong-Min
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- Facile access to 2,2-diaryl 2: H -chromenes through a palladium-catalyzed cascade reaction of ortho -vinyl bromobenzenes with N -tosylhydrazones
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A palladium-catalyzed cascade reaction of ortho-vinyl bromobenzenes with N-tosylhydrazones has been developed, which provides a facile approach to 2,2-disubstituted 2H-chromenes. The migration of palladium from the aryl to vinyl position is crucial, as the in situ produced vinyl palladium intermediate could further react with diazo compounds to generate the reactive species for the sequential annulation. This journal is
- Huang, Xueliang,Yu, Yinghua,Zhang, Heng
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p. 5115 - 5119
(2020/07/23)
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- Opening 2,2-diphenyl-2H-chromene to infrared light
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Time-resolved vibrational spectroscopy studies are reported on the photoinduced structural dynamics of 2,2-diphenyl-2H-chromene, a prototypical photochromic compound that undergoes ring opening upon UV radiation. The transient IR absorption measurements in combination with (TD-)DFT calculations have been used to understand in detail the life cycle of such compounds. Excited-state decay and ring opening was found to occur on an ultrafast time scale. Three species have been identified in the time-resolved IR spectra with two short-lived species (on a picosecond timescale) and a final long-lived species that remains after the measurable ns delay range. These species have been assigned to various open isomers using quantum chemical calculations of equilibrium structures and force fields. From the experiments and calculations key conclusions can be drawn on previously suggested models for the photocycle of such compounds, as well as on possible ways to controllably influence the performance of these compounds.
- Strudwick, Benjamin H.,O'Bryen, Christopher,Sanders, Hans J.,Woutersen, Sander,Buma, Wybren Jan
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p. 11689 - 11696
(2019/06/17)
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- Catalysis by β-Cyclodextrin Hydrate - Synthesis of 2,2-Disubstituted 2H-Chromenes in Aqueous Medium
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A cost-effective, operationally simple and eco-compatible protocol for the one-pot synthesis of photochromic pyrans by the reaction of propargyl alcohols as well as propargyl ethers with differently substituted phenols under ambient atmosphere in aqueous
- Ghatak, Avishek,Khan, Sagar,Bhar, Sanjay
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supporting information
p. 435 - 443
(2016/02/18)
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- A facile synthesis of 2h-chromenes and 9-functionalized phenanthrenes through reactions between α,β-unsaturated compounds and arynes
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Facile syntheses of 2H-chromenes or 9-functionalized phenanthrenes under mild conditions in moderate to good yields have been developed. They each involve annulations of arynes with α,β-unsaturated compounds bearing different electron-withdrawing groups (EWGs). Depending on the natures of the different EWGs, the reactions proceed by different pathways: enals react with arynes through a tandem [2+2] cycloaddition/thermal electrocyclic ring-opening/6e-electrocyclization sequence to afford 2H-chromenes, whereas acyl-/ethoxycarbonyl-/cyano-substituted styrenes undergo Diels-Alder reactions with arynes followed by aromatization to afford 9-functionalized phenanthrenes. The scope, limitations, regioselectivities and mechanisms have been studied and are discussed in detail. Depending on the natures of different EWGs in α,β-unsaturated compounds, the reactions between arynes and α,β-unsaturated compounds proceed by different tandem pathways to afford either 2H-chromenes or 9-functionalized phenanthrenes in a selective manner, which is of potential pharmaceutical interest.
- Zhang, Tiexin,Huang, Xian,Wu, Luling
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experimental part
p. 3507 - 3519
(2012/07/30)
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- Time-Resolved Absorption Studies on the Photochromic Process of 2H-Benzopyrans in the Picosecond to Submillisecond Time Domain
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Picosecond to submillisecond photochromic reactions of 2,4-diphenyl-2H-benzopyran and 2,2,4-triphenyl-2H-benzopyran have been investigated by time-resolved absorption spectroscopy. The C-O bond cleavage of the benzopyrans (closed forms) occurs via the first excited singlet state within 2 ps to produce vibrationally excited open forms in the ground electronic state. In the subnanosecond to submillisecond time domain, several decay components with almost the same spectral profiles are observed. These components are assigned to respective stereoisomers with respect to two double bonds and one single bond of the open enone forms. From the pump-laser power dependencies of the yields of the open forms, it is suggested that the photocleavage gives at first only the open forms revertible to the closed form by a single-bond rotation, and that the photoexcitation of the first generated open forms gives rise to other open forms which need a double-bond rotation for reversion to the closed form. The photochromic reactions of a series of 2H-benzopyrans bearing substituents on the pyran ring have also been studied using nanosecond time-resolved absorption spectroscopy. The size of a substituent in the 4-position fairly affects the rate constants of the thermal reversion of the open form to the closed form.
- Kodama, Yoichi,Nakabayashi, Takakazu,Segawa, Katsunori,Hattori, Emi,Sakuragl, Masako,Nlshi, Nobuyuki,Sakuragi, Hirochika
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p. 11478 - 11485
(2007/10/03)
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