Intramolecular C–H insertion in ring-expanded N-heterocyclic carbenes

Holdroyd, Robert S.; Page, Michael; Warren, Mark R.; Whittlesey, Michael K.

doi:10.1016/j.tetlet.2009.11.090

Cited by 28 publications

(16 citation statements)

References 34 publications

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“…This unanticipated outcome is in stark contrast to the reactions of other heterocarbenes that have been shown to insert into comparable methyl C–H bonds in solution with ease [24]. When the reaction was carried out in an even higher boiling solvent, i.e., nitrobenzene (bp 211 °C), a complicated mixture of decomposition products resulted.…”

Section: Resultsmentioning

confidence: 94%

Intramolecular hydroxycarbene C–H-insertion: The curious case of (o-methoxyphenyl)hydroxycarbene

Gerbig¹,

Ley²,

Reisenauer³

et al. 2010

Beilstein J. Org. Chem.

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SummaryThe first C–H insertion of a hydroxycarbene species in the gas phase has been observed experimentally by means of high vacuum flash pyrolysis (HVFP) and subsequent matrix isolation: (o-Methoxyphenyl)glyoxylic acid gives non-isolable (o-methoxyphenyl)hydroxycarbene upon pyrolysis at 600 °C, which rapidly inserts into the methyl C–H bond. The insertion product, 2,3-dihydrobenzofuran-3-ol, was trapped in an excess of Ar at 11 K and characterized by infrared spectroscopy. The insertion process kinetically outruns the alternative [1,2]H-tunneling reaction to o-anisaldehyde, a type of reaction observed for other hydroxycarbenes. Traces of the dehydration product, benzo[b]furan, were also detected. The potential energy hypersurface including the insertion and hydrogen migration processes was computed at the all-electron coupled-cluster level of theory encompassing single and double substitutions and perturbatively included triple excitations [AE-CCSD(T)] in conjunction with a correlation-consistent double-ζ basis set (cc-pVDZ) by utilizing density functional theory (DFT) optimized geometries (M06-2X/cc-pVDZ) with zero-point vibrational energy (ZPVE) corrections. Exchange of the methoxy for a trifluoromethoxy group successfully prevents insertion and (o-trifluoromethoxy)benzaldehyde is produced instead; however, the carbene cannot be observed under these conditions. Thermal decomposition of (o-methoxyphenyl)glyoxylic acid in refluxing xylenes does not give the insertion product but yields o-anisaldehyde. This unanticipated outcome can be rationalized by protonation of the hydroxycarbene intermediate leading to the tautomeric formyl group. Thermochemical computations at M06-2X/cc-pVDZ in conjunction with a self-consistent solvent reaction field model support this suggested reaction pathway.

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Section: Resultsmentioning

confidence: 94%

Intramolecular hydroxycarbene C–H-insertion: The curious case of (o-methoxyphenyl)hydroxycarbene

Gerbig¹,

Ley²,

Reisenauer³

et al. 2010

Beilstein J. Org. Chem.

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“…Isolable carbenes, in comparison, offer the potential for streamlined syntheses of new classes of highly functionalized substrates without byproduct formation. While stable phosphinosilyl,5 arylamino,6 aminophosphino,7 and diaminocarbenes8, 9 (Figure 1) have been shown to undergo intramolecular CH insertions, the more versatile intermolecular analogues have remained elusive. Indeed, the only examples of intermolecular CH insertions involving isolable carbenes to date have either been metal catalyzed10 or utilized substrates containing relatively acidic CH bonds (p K a ≤25) 11…”

Section: Methodsmentioning

confidence: 99%

N,N′‐Diamidocarbenes Facilitate Selective CH Insertions and Transfer Hydrogenations

Moerdyk

Bielawski

2013

Chemistry A European J

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CH bound: Diamidocarbenes were found to facilitate highly selective CH bond activation in hydrocarbons containing benzylic, allylic, or α‐carbonyl positions. Mechanistic studies showed a preference for intramolecular CH insertion for CH bonds at more substituted carbon atoms, whereas intermolecular insertions were enabled by relatively electron‐deficient substrates. The diamidocarbenes also promoted metal‐ and additive‐free transfer hydrogenations.

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“…[194] Deactivation of the NHC by intra-molecular C-H insertion of the carbene center into a CH3 Mes was proposed to account for the inactivity of the diazepinium-based carbene (Scheme 69). [18,196] Scheme 69. Intra-molecular C-H bond insertion of diazepinium-type NHCs.…”

Section: Polymerizations Directly Induced By Organic Initiatorsmentioning

confidence: 99%

Update and challenges in organo-mediated polymerization reactions

Ottou

Sardón

Mecerreyes

et al. 2016

Progress in Polymer Science

312

223

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International audienceOrganocatalysis has become a very powerful tool for precision macromolecular chemistry, as judged by the number of articles published in this field in the past decade. A variety of small organic molecules, including Bronsted/Lewis bases and acids, based on amines, phosphines or carbenes, but also on bi-component systems, have been employed as a means to catalyze the polymerization of miscellaneous monomers. Not only can organocatalysts be employed to promote the ring-opening polymerization of various heterocyclics (e.g. lactones, lactide, cyclic carbonates, epoxides, lactams, cyclocarbosiloxanes), but some of them also allow activating vinylic monomers such as (meth)acrylics, or triggering the step growth polymerization of monomers such as diisocyanates and diols for polyurethane synthesis. The reduced toxicity of organocatalysts in comparison to their metallic counterparts is also driving their development in some sensitive applications, such as biomedical or microelectronics. Overall, organocatalysts display specific monomer activation modes, thereby providing a unique opportunity to control the polymerization of various functional monomers, under mild conditions. This review article focuses on advances of the past 4 years (>150 publications) in polymerization reactions utilizing small organic molecules either as direct initiators or as true catalysts, with a special emphasis on monomer activation modes, as well as polymerization mechanism aspects

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Intramolecular C–H insertion in ring-expanded N-heterocyclic carbenes

Cited by 28 publications

References 34 publications

Intramolecular hydroxycarbene C–H-insertion: The curious case of (o-methoxyphenyl)hydroxycarbene

Intramolecular hydroxycarbene C–H-insertion: The curious case of (o-methoxyphenyl)hydroxycarbene

N,N′‐Diamidocarbenes Facilitate Selective CH Insertions and Transfer Hydrogenations

Update and challenges in organo-mediated polymerization reactions

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