Generation and Characterization of Alkyl-Substituted m-Xylylenes in Fluid Solution at Room Temperature

Gajewski, Joseph J.; Paul, Gitendra C.; Chang, Ming Jing; Gortva, Andrea M.

doi:10.1021/ja00091a018

Cited by 13 publications

(12 citation statements)

References 2 publications

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“…We then considered α-desilylation of 1-(bromotrimethylsilylmethylene)cyclobutane ( 9 ) as a possible lithium cation-free approach to cyclopentyne according to eq 3. Two groups have reported using this type of elimination to prepare alkylidenecarbenes, although neither has applied it for generating an alkylidenecarbene that might rearrange to a cycloalkyne. To explore this approach to cyclopentyne, the previously unknown 9 was readily prepared in 33% yield by treating bromomethylenecyclobutane with LDA/TMSCl at −107 °C (eq 4).…”

Section: Resultsmentioning

confidence: 99%

Pericyclic Reactions of Free and Complexed Cyclopentyne

1999

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The selectivity between [2 + 2] and [2 + 4] cycloadditions of cyclopentyne with spiro[2.4]nona-2,4-diene depends on the mode of generating the cycloalkyne. Using diazomethylenecyclobutane and (bromocyclobutylidenemethyl)trimethylsilane as precursors affords cyclopentyne in an unencumbered form, whereas using dibromomethylenecyclobutane and 1,2-dibromocyclopentene yields a cyclopentyne-lithium bromide complex.

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Section: Resultsmentioning

confidence: 99%

Pericyclic Reactions of Free and Complexed Cyclopentyne

1999

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“…The tetramethyl- m -xylylene generated by isobutylidene addition to dimethylfulvene is one such case. Our recent work has shown that addition of dioxygen suppresses formation of the dimeric product while not inhibiting generation and reaction of isobutylidene. Unfortunately, both singlet and triplet biradicals are known to react with oxygen so a distinction cannot be made between spin states on the basis of reactivity with oxygen except by comparison with some other reaction that clearly indicates the presence of at least two intermediates.…”

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confidence: 96%

Influence of the Geminal Biscyclopropyl Group in the Reactions of Trimethylenemethane: Reversible Intersystem Crossing

Paul

Gajewski

1996

J. Org. Chem.

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The azo compound precursor to Berson's trimethylenemethane (TMM) biradical system, 2-methylene-1,3-cyclopentanediyl, was substituted with two cyclopropyl groups on the exomethylene. Generation of the TMM species by pyrolysis, direct photolysis, and benzophenone-sensitized photolysis resulted in formation of both cyclopropane ring-opened monomer and cyclopropane ring-unopened dimers whose ratio depended directly on temperature and extent of dilution. The ground state appears to be triplet on the basis of ESR spectrometry. The results contrast with previous work (Waldemar Adam) showing that monocyclopropyl substitution on Berson's TMM species gives both ring-opened monomer and ring-unopened dimers upon pyrolysis and gives mostly ring-unopened dimer upon direct photolysis at 0−20 °C in what appear to be concentration-independent reactions. The observations with the biscyclopropyl-substituted species are consistent with steric effects retarding dimerization of the triplet allowing reversible intersystem crossing back to singlet and perhaps with reduction in the singlet−triplet gap as well.

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“…The reactivity of several derivatives of 2 has also been studied. Gajewski et al . have examined the reactions of alkylated m -xylylenes in solution.…”

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confidence: 99%

Photoelectron Spectroscopy of m-Xylylene Anion

1997

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The 351-nm photoelectron spectrum of the negative ion of 1,3-benzoquinodimethane (m-xylylene) is reported. Features are observed in the photoelectron spectrum corresponding to formation of the 3B2, 1A1, and 1B2 states of m-xylylene. The electron affinity of the triplet ground state is found to be 0.919 ± 0.008 eV, and vibrational frequencies of 290, 540, and 1500 cm-1 are obtained. The active modes are assigned to α-carbon bending, ring deformation, and methylene bending, respectively. The 1A1 state is found to lie 9.6 ± 0.2 kcal/mol higher in energy than the ground state, in good agreement with theoretical predictions. Vibrational frequencies of 265, 1000, and 1265 cm-1 are found for this state. The 1B2 is estimated to be <21.5 kcal/mol higher in energy than the ground state. Density functional calculations have been carried out on the negative ion, indicating that the 2B1 ion is a minimum on the potential energy surface, lying 2.9 kcal/mol lower in energy than the 2A2 ion, which is a transition state.

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Generation and Characterization of Alkyl-Substituted m-Xylylenes in Fluid Solution at Room Temperature

Cited by 13 publications

References 2 publications

Pericyclic Reactions of Free and Complexed Cyclopentyne

Pericyclic Reactions of Free and Complexed Cyclopentyne

Influence of the Geminal Biscyclopropyl Group in the Reactions of Trimethylenemethane: Reversible Intersystem Crossing

Photoelectron Spectroscopy of m-Xylylene Anion

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