Roles of multiplicity and electronic excitation on intramolecular reactions of alkylcarbenes in condensed phase

Chang, K. T.; Shechter, H.

doi:10.1021/ja00511a058

Cited by 63 publications

(20 citation statements)

References 2 publications

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“…Photolysis of ethylmethyldiazirine gives a more complex mixture of products than observed upon pyrolysis of the same precursor. Many more examples of this type were subsequently reported by Shechter and Jones. , …”

Section: Discussionmentioning

confidence: 85%

Study of trans-2-tert-Butylcyclopropylcarbene by Laser Flash Photolysis and Chemical Analysis¹

and

Platz

1998

J. Am. Chem. Soc.

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Laser flash photolysis (LFP) of trans-2-tert-butylcyclopropyldiazirine (4) produces trans-2-tert-butylcyclopropylcarbene (5). Carbene 5 can be trapped with pyridine to form ylide 6. The rate of formation of ylide 6 was resolved and found to be linearly dependent on the concentration of pyridine. The lifetime of carbene 5 was determined to be 22 ns (pentane), 18 ns (acetonitrile and CF2ClCFCl2), 15 ns (cyclohexane), and 27 ns (cyclohexane-d 12) at ambient temperature. The lifetime of carbene 5 in solution, at ambient temperature, is controlled substantially by reaction with solvent and only to a minor extent by rearrangement to cyclobutene 7. Photolysis of 4 (350 nm) in Freon-113 produces 3-tert-butylcyclobutene (7) along with products derived from attack of the carbene on solvent. Photolysis of 4 in the presence of trapping agents (tetramethylethylene, cyclopentene, propylamine, trifluoroethanol) produces adducts with little or no corresponding decrease in the yield of 7. The preferred interpretation is that cyclobutene 7 is formed by a rearrangement of the excited state of the diazirine (diazirinyl biradical), and not by a carbenic process at 0 °C and lower temperatures. This mechanism is supported by product analysis of a non-nitrogenous cyclopropylcarbene precursor. At ambient temperature, cyclobutene 7 is formed by both diazirine excited state (diazirinyl biradical) and carbene rearrangement.

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Section: Discussionmentioning

confidence: 85%

Study of trans-2-tert-Butylcyclopropylcarbene by Laser Flash Photolysis and Chemical Analysis¹

and

Platz

1998

J. Am. Chem. Soc.

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“…The long-recognized problem of detangling the chemistry of carbenes from the reactions of their precursors remains incredibly relevant today. ,,− The field of chemical biology will benefit from future studies to develop photoaffinity tags with desirable physiochemical properties that can label biological targets via a “real” carbene insertion mechanism.…”

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confidence: 99%

Probing the Mechanism of Photoaffinity Labeling by Dialkyldiazirines through Bioorthogonal Capture of Diazoalkanes

et al. 2020

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Dialkyldiazirines have emerged as reagents of choice for biological photoaffinity labeling studies. The mechanism of crosslinking has dramatic consequences for biological applications where instantaneous labeling is desirable, as carbene insertions display different chemoselectivity and are much faster than competing mechanisms involving diazo or ylide intermediates. Here, deuterium labeling and diazo compound trapping experiments are employed to demonstrate that both carbene and diazo mechanisms operate in the reactions of a dialkyldiazirine motif that is commonly utilized for biological applications. For the fraction of intermolecular labeling that does involve a carbene mechanism, direct insertion is not necessarily involved, as products derived from a carbonyl ylide are also observed. We demonstrate that a strained cycloalkyne can intercept diazo compound intermediates and serve as a bioorthogonal probe for studying the contribution of the diazonium mechanism of photoaffinity labeling on a model protein under aqueous conditions.

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“…1 While the involvement of excited states of diazirines and diazo compounds can complicate the situation in the photolytic decompositions, it is generally agreed that singlet carbenes, as the first-formed intermediates in thermal processes, can yield insertion and rearrangement products. 2 The complexities of the formation and reactions of tert-butylmethylene have been summarized in a paper by Glick and co-workers.…”

Section: Introductionmentioning

confidence: 99%

A QTAIM and Electron Delocalization Computational Study oftert-Butylmethylene, Trimethylsilylmethylene, and Trimethylgermylmethylene. A New Method for Unambiguously Characterizing the Bonding between Pairs of Atoms in Reaction Intermediates

Poulsen

2005

J. Chem. Theory Comput.

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While studies on the experimental photolytic and thermolytic extrusion of nitrogen from tert-butyldiazomethane and tert-butyldiazirine and the decomposition of other precursors have shown a mixture of C-H and C-C insertion products depending on conditions, the analogous trimethylsilyldiazomethane undergoes solely Si-C insertion. Description of the singlet tert-butylmethylene intermediates potentially involved in the C-H and C-C insertion reactions and were addressed through computational means by Armstrong et al. (J. Am. Chem. Soc. 1995, 117, 3685-3689). In addition to re-examining singlet tert-butylmethylene at a higher level of theory [CCSD/6-311+G(d,p)], we have studied the silicon and germanium analogues trimethylsilylmethylene and trimethylgermylmethylene. A computational atoms-in-molecules and atomic-basin-delocalization-indices analysis established that the singlet carbenes, while exhibiting varying degrees of delocalization, are not bridged species based on the fact that none possess a pentacoordinate methyl group. In addition, from the results, we are able to make a prediction of solely a Ge-C insertion product for the extrusion of nitrogen from trimethylgermyldiazomethane. Most importantly, we demonstrated that a combination of quantum theory of atoms in molecules (QTAIM) molecular graphs, the evaluation of delocalization indices, and a visualization of the closeness of atomic basins [Formula: see text] a QTAIM-DI-VISAB analysis [Formula: see text] should be considered as the method of choice for unambiguously characterizing the bonding between pairs of atoms not only of carbenes but of other reaction intermediates such as carbocations, carbanions, and radicals.

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Roles of multiplicity and electronic excitation on intramolecular reactions of alkylcarbenes in condensed phase

Cited by 63 publications

References 2 publications

Study of trans-2-tert-Butylcyclopropylcarbene by Laser Flash Photolysis and Chemical Analysis¹

Study of trans-2-tert-Butylcyclopropylcarbene by Laser Flash Photolysis and Chemical Analysis¹

Probing the Mechanism of Photoaffinity Labeling by Dialkyldiazirines through Bioorthogonal Capture of Diazoalkanes

A QTAIM and Electron Delocalization Computational Study oftert-Butylmethylene, Trimethylsilylmethylene, and Trimethylgermylmethylene. A New Method for Unambiguously Characterizing the Bonding between Pairs of Atoms in Reaction Intermediates

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Roles of multiplicity and electronic excitation on intramolecular reactions of alkylcarbenes in condensed phase

Cited by 63 publications

References 2 publications

Study of trans-2-tert-Butylcyclopropylcarbene by Laser Flash Photolysis and Chemical Analysis1

Study of trans-2-tert-Butylcyclopropylcarbene by Laser Flash Photolysis and Chemical Analysis1

Probing the Mechanism of Photoaffinity Labeling by Dialkyldiazirines through Bioorthogonal Capture of Diazoalkanes

A QTAIM and Electron Delocalization Computational Study oftert-Butylmethylene, Trimethylsilylmethylene, and Trimethylgermylmethylene. A New Method for Unambiguously Characterizing the Bonding between Pairs of Atoms in Reaction Intermediates

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Study of trans-2-tert-Butylcyclopropylcarbene by Laser Flash Photolysis and Chemical Analysis¹

Study of trans-2-tert-Butylcyclopropylcarbene by Laser Flash Photolysis and Chemical Analysis¹