Hydrazone-Initiated Carbene/Alkyne Cascades to Form Polycyclic Products: Ring-Fused Cyclopropenes as Mechanistic Intermediates

Le, Phong Q.; May, Jeremy A.

doi:10.1021/jacs.5b08157

Cited by 68 publications

(36 citation statements)

References 44 publications

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“…On the other hand, cascade reactions involving carbene/alkyne metathesis (CAM) have shown high efficiency for the bond formations in the direct construction of polycyclic frameworks . Compared to the studies with diazo compounds as the carbene precursor in CAM transformations, using other readily available and more stable substrates as the initiator, such as hydrazone– or triazole,– is rare. Recently, the cascade transformation of alkyne tethered N ‐sulfonyl hydrazone is reported by May′s group via a cyclopropene intermediate in the presence of Rh 2 (esp) 2 catalyst (Scheme b) .…”

Section: Figurementioning

confidence: 99%

“…Compared to the studies with diazo compounds as the carbene precursor in CAM transformations, using other readily available and more stable substrates as the initiator, such as hydrazone– or triazole,– is rare. Recently, the cascade transformation of alkyne tethered N ‐sulfonyl hydrazone is reported by May′s group via a cyclopropene intermediate in the presence of Rh 2 (esp) 2 catalyst (Scheme b) . The intermolecular version, which is a cobalt‐catalyzed metalloradical approach, is presented by Zhang and Bruin for the direct synthesis of 2 H ‐chromenes (Scheme c) .…”

Section: Figurementioning

confidence: 99%

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Copper‐ or Thermally Induced Divergent Outcomes: Synthesis of 4‐Methyl 2H‐Chromenes and Spiro‐4H‐Pyrazoles

Zheng

Qiu

Hong

et al. 2017

Chemistry A European J

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An unprecedented divergent outcome transformation of alkyne tethered N-sulfonyl hydrazones is reported, which provides a direct and effective access to 4-methyl 2H-chromene derivatives and spiro-4H-pyrazoles in the presence of copper catalyst or under thermal conditions, respectively. The notable features of this process include readily available starting materials, an inexpensive copper catalyst, mild reaction conditions, broad substrate scope, diverse transformations and potential applications of these generated products. Mechanistic studies indicate that the 3H-pyrazole, which is generated via direct [3+2] cycloaddition, is the communal key intermediate of these two divergent transformations. To the best of our knowledge, this is the only example of sulfonation reaction that goes through a cascade process involving 3H-pyrazole, which was isolated and confirmed by single crystal X-ray diffraction analysis for the first time.

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Section: Figurementioning

confidence: 99%

Section: Figurementioning

confidence: 99%

Copper‐ or Thermally Induced Divergent Outcomes: Synthesis of 4‐Methyl 2H‐Chromenes and Spiro‐4H‐Pyrazoles

Zheng

Qiu

Hong

et al. 2017

Chemistry A European J

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“…The high strain energy of ring-fused cyclopropenes makes their synthesis andi solation ad ifficult task. [26] We attempted to apply our method to attain this aim. After severalt rials, we eventually isolated an eight-memberedf used cyclopropene 7a in am oderate yield (42 %) starting from N-nosylhydrazone 6a, in ad iluted solution (0.03 m).…”

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confidence: 88%

Silver-Catalyzed Cyclopropanation of Alkenes Using N-Nosylhydrazones as Diazo Surrogates

et al. 2017

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An efficient silver-catalyzed [2 + 1] cyclopropanation of sterically hindered internal alkenes with diazo compounds in which room-temperature-decomposable N-nosylhydrazones are used as diazo surrogates is reported. The unexpected unique catalytic activity of silver was ascribed to its dual role as a Lewis acid activating alkene substrates and as a transition metal forming silver carbenoids. A wide range of internal alkenes, including challenging diarylethenes, were suitable for this protocol, thereby affording a variety of cyclopropanes with high efficiency in a stereoselective manner under mild conditions.

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“…The high strain energy of ring‐fused cyclopropenes makes their synthesis and isolation a difficult task . We attempted to apply our method to attain this aim.…”

Section: Figurementioning

confidence: 99%

Silver‐Catalyzed [2+1] Cyclopropenation of Alkynes with Unstable Diazoalkanes: N‐Nosylhydrazones as Room‐Temperature Decomposable Diazo Surrogates

Liu

Liao

et al. 2017

Chemistry A European J

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The [2+1] cycloaddition of alkynes with diazo compounds represents one of the most powerful and reliable methods for the construction of cyclopropenes. However, it remains a formidable challenge to accomplish the cyclopropenation of alkynes with non-stabilized diazoalkanes, owing to the fact that such compounds are unstable and prone to detonation. Herein, we report a general silver-catalyzed cyclopropenation reaction of alkynes with unstable diazoalkanes, by for the first time the discovery and application of N-nosylhydrazones as room-temperature decomposiable diazo surrogates. This method allows for the efficient assembly a wide variety of cyclopropene derivatives that are otherwise difficult to access by conventional methods.

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Hydrazone-Initiated Carbene/Alkyne Cascades to Form Polycyclic Products: Ring-Fused Cyclopropenes as Mechanistic Intermediates

Abstract: A hydrazone-based carbene/alkyne cascade produced a variety of bridged and fused polycyclic products. NaOSiMe3 is a superior base for conversion of hydrazones to diazoalkanes. A key mechanistic intermediate, a ring-fused cyclopropene, has been isolated and characterized.

Cited by 68 publications

References 44 publications

Copper‐ or Thermally Induced Divergent Outcomes: Synthesis of 4‐Methyl 2H‐Chromenes and Spiro‐4H‐Pyrazoles

Copper‐ or Thermally Induced Divergent Outcomes: Synthesis of 4‐Methyl 2H‐Chromenes and Spiro‐4H‐Pyrazoles

Silver-Catalyzed Cyclopropanation of Alkenes Using N-Nosylhydrazones as Diazo Surrogates

Silver‐Catalyzed [2+1] Cyclopropenation of Alkynes with Unstable Diazoalkanes: N‐Nosylhydrazones as Room‐Temperature Decomposable Diazo Surrogates

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