Silyl-substituted cyclopropyl carbenoids

Creary, Xavier; Jiang, Ziqi; Butchko, Mark A.; Mclean, K.

doi:10.1016/0040-4039(95)02266-x

Cited by 20 publications

(19 citation statements)

References 9 publications

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“…We and others , have been interested in the chemistry of carbenes that contain silicon in the proximity of the carbenic center. This interest grows out of our finding that silicon has a high propensity to migrate to carbenic centers.…”

Section: Introductionmentioning

confidence: 99%

The Bicyclo[2.2.2]octyl Carbene System as a Probe for Migratory Aptitudes of Hydrogen to Carbenic Centers

Creary

Butchko

2001

J. Am. Chem. Soc.

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A series of tosylhydrazone derivatives of exo-6-substituted bicylo[2.2.2]octan-2-ones have been prepared. Thermal decomposition of the sodium salts of these tosylhydrazones gives carbene-derived products from 1,3-migration of either the C6 hydrogen (perturbed) or the C7 hydrogen (unperturbed), along with smaller amounts of alkenes derived from 1,2-hydrogen migration. The exo-6-substituent strongly activates 1,3-hydrogen migration in the case of SiMe(3) and weakly activates it in the case of CH(3) substitution. Thiomethoxy and carbomethoxy are weakly deactivating, while cyano and methoxy groups are strongly deactivating. B3LYP/6-31G* calculations on these substituted carbenes and transition states are in qualitative agreement with the ease of 1,3-hydrogen migration of perturbed vs unperturbed hydrogen. These experimental results and computational studies suggest carbene stabilization due to the exo-6-silyl group. They also suggest a reactant-like transition state for 1,3-hydrogen migration in which the inductive effect influences ease of migration. In the case of the exo-6-methoxy group, the inductive effect overwhelms any potential resonance-stabilizing effects.

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Section: Introductionmentioning

confidence: 99%

The Bicyclo[2.2.2]octyl Carbene System as a Probe for Migratory Aptitudes of Hydrogen to Carbenic Centers

Creary

Butchko

2001

J. Am. Chem. Soc.

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“…The enhanced reactivity of captodative alkenes has been noted in radical 193 ± 199 and [2+2]-cycloaddition 45, 199 ± 202 reactions. The captodative acceleration was considered to be the reason explaining the results obtained in studies of cyclisation of 6-substituted hex-5-en-1-yl radical, 203 homosolvolysis of some alkyl bromides on treatment with di-tert-butylnitroxide, 204 thermal rearrangement of substituted 2-arylmethylenecyclopropanes, 205 isomerisation of diastereomeric substituted cyclopropanes 206,207 and thermal homolysis of the C7C bond in hexa-1,5-dienes 207 and dibenzyls. 208,209 EPR data for substituted benzyl radicals point to enhanced stabilisation of those radicals that contain both electron-donating and electron-withdrawing substituents, whereas two identical substituents decrease radical stabilisation.…”

Section: Critical Analysis Of the Existing Approachesmentioning

confidence: 99%

Correlation analysis in the chemistry of free radicals

Cherkasov¹,

Jönsson²,

Галкин³

et al. 2001

Russ. Chem. Rev.

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Published data now available on the use of correlation Published data now available on the use of correlation analysis in free-radical chemistry are discussed systematically. The analysis in free-radical chemistry are discussed systematically. The scales of `radical' scales of `radical' s s-constants of substituents proposed previously -constants of substituents proposed previously are analysed. It is shown that none of them is applicable as a are analysed. It is shown that none of them is applicable as a general scale because almost in all cases, it is impossible to general scale because almost in all cases, it is impossible to separate correctly the proper radical and polar contributions to separate correctly the proper radical and polar contributions to the overall effect of substituents. A new approach to the quanti-the overall effect of substituents. A new approach to the quantitative estimation of the relationship between the structure and tative estimation of the relationship between the structure and reactivity of molecules in free-radical processes called reactivity of molecules in free-radical processes called r r 7 72 2 -analysis -analysis is proposed. The bibliography includes 238 references. is proposed. The bibliography includes 238 references.

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“…We and others 6 have been interested in the chemistry of carbenes containing silicon in adjacent and more remote positions relative to the carbenic center. Our previous studies have shown that the trimethylsilyl group undergoes very facile migration to carbenic centers.…”

Section: Introductionmentioning

confidence: 99%

“…Our previous studies have shown that the trimethylsilyl group undergoes very facile migration to carbenic centers. The alkene 8 derived from silyl migration is the major product formed from carbene 7 ,5a while the silyl migration product 10 is formed exclusively from 9 5b. With these results in mind, we wanted to determine the fate of cyclopropyl carbenes with silicon in the β-position as in 11 and 12 .…”

Section: Introductionmentioning

confidence: 99%

β-Trimethylsilyl Cyclopropylcarbenes

Creary

Butchko

2001

J. Org. Chem.

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Thermal decomposition of the in situ generated lithium salt of the tosylhydrazone derivative of cyclopropyl trimethylsilylmethyl ketone gave 1-cyclopropyl-1-trimethylsilylethylene, a product of exclusive silyl migration. Thermal decomposition of the sodium salts of tosylhydrazone derivatives of 1-trimethylsilylcyclopropyl alkyl ketones also gave methylenecyclopropane products derived from trimethylsilyl migration. These reactions were interpreted in terms of rapid trimethylsilyl migration to carbene-like centers that compete effectively with ring expansion processes of cyclopropylcarbenes. Computational studies (B3LYP/6-31G) suggest that cyclopropyl stabilization of carbenes is more effective than beta-trimethylsilyl stabilization. However, beta-trimethylsilyl stabilized conformations are easily attained, and these conformations can lead to silyl migrations. There are two minimum energy conformations of methyl-1-trimethylsilylcyclopropylcarbene, 27, and the rotational barrier to interconversion of these conformations (5.4 kcal/mol) is substantially lower than in the parent cyclopropylcarbene (15 kcal/mol). The onset of a stabilizing interaction in the transition state between the carbene vacant orbital with the adjacent Si-C sigma-orbital is proposed. Computational studies also show a very small (2.0 kcal/mol) barrier for trimethylsilyl migration in trimethylsilylmethyl cyclopropylcarbene, 11.

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Silyl-substituted cyclopropyl carbenoids

Cited by 20 publications

References 9 publications

The Bicyclo[2.2.2]octyl Carbene System as a Probe for Migratory Aptitudes of Hydrogen to Carbenic Centers

The Bicyclo[2.2.2]octyl Carbene System as a Probe for Migratory Aptitudes of Hydrogen to Carbenic Centers

Correlation analysis in the chemistry of free radicals

β-Trimethylsilyl Cyclopropylcarbenes

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