Palladium-catalyzed annulation of alkynyl aryl ethers with isocyanates through o-C–H cleavage. Synthesis of solid-state emissive 2-methylidene-2H-1,4-benzoxazin-3(4H)-ones

Minami, Yasunori; Kanda, Mayuko; Sakai, Megumi; Hiyama, Tamejiro

doi:10.1016/j.tet.2015.02.062

Cited by 14 publications

(8 citation statements)

References 101 publications

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“…However, without Zn, product 14a was obtained with perfect regioselectivity in moderate yield. 21,22 With Zn(OAc) 2 cocatalyst, the reaction was accelerated and the yield of 14a increased (Scheme 12). 23 Purification of 14a was easily performed by preparative TLC followed by recrystallizations from CH 2 Cl 2 /hexane.…”

Section: Reaction With Isocyanates: Synthesis Of Solid-state Emissive...supporting

confidence: 83%

“…Ethyl phenyl ketene (15) reacted with 1b regioselectively in the presence of Pd(OAc) 2 , PCy 3 , and Zn(OAc) 2 to give 1benzopyran-3-one 16 (Scheme 16). 22,27 The product 16, which is a carbon analogue of 14, hardly emitted luminescence (Φ f < 0.01) in cyclohexane.…”

Section: Reaction With Ketenesmentioning

confidence: 99%

“…Incidentally, we attempted the reaction of 1b with phenyl isocyanate ( 13a ) in the presence of Pd(OAc) 2 /PCy 3 /Zn but observed no desired product. However, without Zn, product 14a was obtained with perfect regioselectivity in moderate yield. , With Zn(OAc) 2 cocatalyst, the reaction was accelerated and the yield of 14a increased (Scheme ). Purification of 14a was easily performed by preparative TLC followed by recrystallizations from CH 2 Cl 2 /hexane.…”

Section: Sequential Insertion/annulation Of Aryl Ethynyl Ethers With ...mentioning

confidence: 99%

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Synthetic Transformations through Alkynoxy–Palladium Interactions and C–H Activation

Minami

Hiyama

2015

Acc. Chem. Res.

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Organic synthesis based on straightforward transformations is essential for environmentally benign manufacturing for the invention of novel pharmaceuticals, agrochemicals, and organoelectronic materials in order to ultimately realize a sustainable society. Metal-catalyzed C-H bond-cleaving functionalization has become a promising method for achieving the above goal. For site-selective C-H bond cleavage, so-called directing groups, i.e., ligands attached to substrates, are employed. Commonly utilized directing groups are carbonyls, imines, carboxyls, amides, and pyridyls, which σ-donate electron pairs to metals. On the other hand, unsaturated substrates such as alkenes and alkynes, which participate largely as reactants in organic synthesis, are prepared readily by a wide variety of synthetic transformations and are also employed as reactants in organometallic chemistry. Moreover, such unsaturated groups form complexes with some metals by ligation of their p orbitals via donation and back-donation. However, the use of unsaturated bonds as directing groups has not been studied extensively. We have been involved in the development of methods for the cleavage of C-H bonds by means of transition-metal catalysts to achieve new carbon-carbon bond-forming reactions and incidentally came to focus on the alkynoxy group (-OC≡C-), which shows a ketene-like resonance structure. We expected the alkynoxy group to interact electrophilically with a low-valent transition-metal complex in order to cleave adjacent C-H bonds. In this Account, we summarize our recent achievements on C-H activation based on interactions of palladium with the alkynoxy group in alkynyl aryl ethers. The alkynoxy group plays two roles in the transformation: as a directing group for adjacent C-H bond activation and as an acceptor for the carbon and hydrogen fragments. A typical example is palladium-catalyzed ortho-C-H bond activation in alkynoxyarenes followed by sequential insertion/annulation with internal alkynes and the alkynoxy group to produce 2-methylidene-2H-1-benzopyrans. Mechanistic studies have shown that the presence of both oxygen and alkynyl moieties is essential for selective ortho-C-H bond activation and subsequent annulation. In addition to internal alkynes, norbornene, allenes, isocyanates, and ketenes produce the corresponding oxacycles. It is worthy of note that benzoxadinones formed by the reaction with isocyanates exhibit solid-state luminescence. In addition, 2-methylphenyl alkynyl ethers and 2-alkynoxybiaryls undergo intramolecular annulation at the benzylic γ-position and aryl δ-position via C-H bond activation to give benzofurans and dibenzopyrans, respectively. The disclosed methods allow us to construct useful π-conjugated systems in a straightforward manner.

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Section: Reaction With Isocyanates: Synthesis Of Solid-state Emissive...supporting

confidence: 83%

Section: Reaction With Ketenesmentioning

confidence: 99%

Section: Sequential Insertion/annulation Of Aryl Ethynyl Ethers With ...mentioning

confidence: 99%

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Synthetic Transformations through Alkynoxy–Palladium Interactions and C–H Activation

Minami

Hiyama

2015

Acc. Chem. Res.

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“…In particular, activation of C–H bonds of arenes and coupling with various π-bonds/electrophilic molecules such as alkynes, carbene precursors, alkenes, strained/reactive rings, isocyanates, allenes, and imines were extensively explored for construction of diverse cyclic functional molecules. Although ketenes are highly electrophilic with two π-bonds and have been well-studied in organic synthesis, they have been rarely employed as a coupling partner in C–H activation systems …”

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confidence: 99%

Access to Quaternary Stereogenic Centers via Rhodium(III)-Catalyzed Annulations between 2-Phenylindoles and Ketenes

Yang

Kong

et al. 2018

Org. Lett.

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“…Despite their high activity, the corresponding catalytic transformations in C–H activation chemistry largely lag behind. The insertion of arene C–H bonds into polar unsaturated bonds via C–H activation has been well-studied, and we have also successfully achieved acylation of arenes via insertion of a C–H bond into the CC bond of ketenes under redox-neutral conditions . Recently, the Zeng group reported cyclization of N -nitrosoanilines with α-diazo-β-ketoesters through a cobalt(III)-catalyzed C–H activation/Wolff rearrangement, in which a ketene was established as a key intermediate via a Co-mediated rearrangement of carbenes .…”

mentioning

confidence: 99%

Redox-Neutral Access to Isoquinolinones via Rhodium(III)-Catalyzed Annulations of O-Pivaloyl Oximes with Ketenes

Yang

Liu

et al. 2018

Org. Lett.

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Palladium-catalyzed annulation of alkynyl aryl ethers with isocyanates through o-C–H cleavage. Synthesis of solid-state emissive 2-methylidene-2H-1,4-benzoxazin-3(4H)-ones

Cited by 14 publications

References 101 publications

Synthetic Transformations through Alkynoxy–Palladium Interactions and C–H Activation

Synthetic Transformations through Alkynoxy–Palladium Interactions and C–H Activation

Access to Quaternary Stereogenic Centers via Rhodium(III)-Catalyzed Annulations between 2-Phenylindoles and Ketenes

Redox-Neutral Access to Isoquinolinones via Rhodium(III)-Catalyzed Annulations of O-Pivaloyl Oximes with Ketenes

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